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Development of An Alpha Silicon Carbide Based Liquid Toner for Electro-Photographic Solid Freeform Fabrication


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DEVELOPMENT OF AN ALPHA SILICON CARBIDE BASED LIQUID TONER FOR ELECTRO-PHOTOGRAPHIC SOLID FREEFORM FABRICATION By NAVIN JOSE MANJOORAN A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003

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This document is dedicated to my fath er, my mother and my brother Neil.

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iii ACKNOWLEDGEMENTS This paper is the fruit of the enduring s upport, love and cooper ation of my mother Mrs. Grace Jose and father Mr. Jose Manj ooran. Although they are thousands of miles away, they have been unshakable pillars of support, helping me fight and win every battle. Their faith in my abilities has been my strength and their visions my inspiration. All those words of wisdom have been my driv ing force through all those hard times. No words said can express how indebted I am to them for what I am today and for what I shall accomplish in the future. I would also like to thank my brother, Neil, for being there and helping to keep me going on and on. Joy uncle, Elizabeth a unty, Varkeychan uncle, Minna aunty, Thomachan uncle, Lizy aunty, Tony uncle and Devi aunty have given me the strength and the endurance to complete what I started and the motivation to excel in it. They have been my “safety net” thr oughout my graduate education. Dr. Sigmund, my advisor, my teacher, my supervisor and my mentor, taught me more than I ever hoped to learn here at graduate school. His work has been my inspiration. This work has been a product of his patience and endurance. He has inspired me to be a better researcher and also a be tter person. He understood my problems and has helped me to succeed in spite of them. My success is and will be a reflection of his outstanding abilities as a teacher. I hope to do my best in whatever task I undertake and always strive for perfection, as a tribute to him. Nothing short of this will be adequate to express my gratitude to him.

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iv I would like to thank Dr. Zaman for all the support he has gi ven me through the entire project. His support and cooperation all through the project helped me immensely. I am grateful to Dr. Butt for agreeing to be on my committee and giving me valuable suggestions. I would also like to thank Dr. Ku mar, for constantly guiding me with my experiments and for always being ready to help. Words cannot express my gratitude for my fr iends here in Gainesville, for always being there when I needed them most. A bhishek, Agam, Ajay, Amit, Amol, Amrita, Anagha, Bharti, Bullet, Devraj, Dhruv, Gargi, Jairaj, Jason, Javid, Jayashree, Joanne, Joyti, Kunal, Lal, Nova, Nyla, Priya, Sajan, Sidd, Sudeep, Sandeep, Sandy, Seemanth, Seethu, Shruti, Sonali, Soumya, Teena, Thrit y, Unnat, Vijayram, Vi vek and the entire graduating class of 2003. I would also like to thank all the students in our research group “Dr. Sigmund’s Research Group” for being the greatest group ever-helpful, supportive and understanding. I would also like to th ank the entire Materials Science and Engineering Department for making this possible.

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v TABLE OF CONTENTS page ACKNOWLEDGEMENTS...............................................................................................iii LIST OF FIGURES.........................................................................................................viii ABSTRACT......................................................................................................................x ii CHAPTER 1 INTRODUCTION........................................................................................................1 2 GENERAL THEORIES AND CONCEPTS IN SOLID FREEFORM FABRICATION...........................................................................................................3 History........................................................................................................................ ..3 What Is SFF?................................................................................................................3 3 BASIC THEORIES AND CONCEPTS IN COLLOIDAL PROCESSING.................9 Stabilization Methods for Colloids...............................................................................9 Electrostatic Stabilization....................................................................................10 Double Layer Repulsion......................................................................................12 DLVO Theory.....................................................................................................12 Polymeric Stabilization.......................................................................................12 Electrosteric Stabilization....................................................................................13 Coagulation.................................................................................................................14 4 BASIC CONCEPTS AND THEORIES IN UNDERSTANDING THE RHEOLOGICAL PROPERTIES FO R PARTICULATE SUSPENSIONS...............15 Importance of Rheological properties........................................................................15 Solids Loading............................................................................................................16 Particle Size Analysis.................................................................................................18 Polymer Adsorbed Layers..........................................................................................18 5 METHODOLOGY FOR LIQUID TONER MATERIAL SELECTION...................20 Solvent–Selection Methodology.................................................................................20 Ceramic Particles–Selection Methodology.................................................................20 Dispersing Agent–Selection Methodology.................................................................21

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vi Charge Controlling Agents–Selection Methodology..................................................24 6 RAW MATERIALS CHARACTE RIZATION AND EXPERIMENTAL TECHNIQUES...........................................................................................................25 Scanning Electron Microscopy (SEM )......................................................................25 Energy Dispersive x-ray Spectrometry (EDS)...........................................................27 Nuclear Magnetic Resonance Spectroscopy (NMR)..................................................28 Planetary Ball Mill......................................................................................................29 Misonix Sonicator 3000..............................................................................................30 Suspension Preparation...............................................................................................30 Rheometer...................................................................................................................30 Viscosity Measurements.............................................................................................31 Optical Density Measurement Equipment Setup........................................................31 7 EFFECT OF POLYMER ADSORPTION ON RHEOLOGY AND SOLIDS LOADING OF THE SUSPENSION..........................................................................33 Determination of the Optim um Amount of Polymer..................................................33 Optimum Amount of Polystyrene.......................................................................33 Optimum Amount of LP1....................................................................................33 Optimum Amount of Polybutadiene...................................................................34 Comparison of the Optimum Amounts of Dispersants.......................................36 Determination of the Optimum Amount of Charge Controlling Agent.....................36 Optimum Amount of CCA7 in the LP1 suspension............................................37 Optimum amount of CCA7 in the Polystyrene Suspension................................37 Comparison of the Opt imum Amounts of CCA..................................................38 8 EFFECT OF RELATIVE VISCOSIT Y ON SOLIDS LOADING OF THE NON POLAR SILICON CARBIDE SUSPENSION...........................................................40 Relative Viscosity on Solids Loading for the Polybutadiene Stabilized Suspension.............................................................................................................41 Relative Viscosity on Solids Loading Dependence for the LP1 Stabilized Suspension.............................................................................................................42 Solids Loading Dependence on Relative Viscosity for the Polystyrene Stabilized Suspension.............................................................................................................43 Comparison of the Stabilization Methods..................................................................44 9 EFFECT OF OPTICAL DENS ITY VARIANCE WITH VOLTAGE.......................46 Optical Density Variance with Voltage for LP1.........................................................46 Optical Density Variance with Voltage for Polystyrene............................................49 Comparison of Optical Density Variance wi th Voltage for LP1 and Polystyrene.....51 10 EFFECT OF OPTICAL DENSITY VARIANCE WITH TIME................................54

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vii Optical Density Variance with Time for LP1.............................................................54 Optical Density Variance with Time for Polystyrene.................................................56 Comparison of Optical Density Variance with Time for LP1 and Polystyrene.........58 11 ANALYSIS OF THE ELECTR OPHORETIC DEPOSITION...................................60 Scanning Electron Microscope Images......................................................................61 Polystyrene Samples............................................................................................61 LP1 Samples........................................................................................................63 Digital Camera Pictures..............................................................................................64 12 CONCLUSION...........................................................................................................69 LIST OF REFERENCES...................................................................................................71 BIOGRAPHICAL SKETCH.............................................................................................74

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viii LIST OF FIGURES Figure page 2-1 Block diagram of the principle of the solid freeform fabrication (SFF) technique....4 2-2 The stereo lithographic machine................................................................................5 2-3 The electro-photographic solid free form fabrication (ESFF) machine......................6 2-4 A schematic of the electro-photographi c solid freeform fabrication (ESFF) machine .....................................................................................................................7 2-5 A sketch showing the principle of the electro-photographic solid freeform fabrication (ESFF) machine.......................................................................................7 3-1 The double layer consisting of the three regions......................................................11 3-2 The variation of potential energy between two particles in a liquid medium due to van der Waals attraction and el ectric double layer repulsion...................................13 4-1 The variation of shear stress and viscosity with shear rate......................................16 5-1 The chemical structures for tr ans and cis decahydronapthalene..............................21 5-2 Separation distance (nm) for SiC partic les with the van der Waals interaction energy (kT) in the sphere-sphere interaction mode..................................................23 6-1 SEM picture of the 6H-alpha silicon carbide (UF Grade 15).................................26 6-2 SEM picture of the charge controlling agent (CCA7)..............................................27 6-3 EDS of the charge controlling agent 7 (CCA7).......................................................27 6-4 The carbon (13C) NMR for the LP1 polymer...........................................................28 6-5 The proton (1H) NMR for the LP1 polymer.............................................................29 6-6 Flowchart for the suspension preparation................................................................32 7-1 Optimum amount of polystyrene require d for complete coverage of the SiC surface......................................................................................................................34

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ix 7-2 Optimum amount of LP1 required for co mplete coverage of the SiC surface.........35 7-3 Optimum amount of polybutadiene requi red for complete coverage of the SiC surface......................................................................................................................35 7-4 5 vol% SiC in decahydr onapthalene with varying amounts of the dispersants polystyrene(PS), polybutadiene(PB) and LP1 used.................................................36 7-5 The amount of LP1 added is 0.4 wt% SiC for the 5 vol% SiC in decahydronapthalene. The deposition was done for 60 seconds and the DC voltage applied was +4kV........................................................................................38 7-6 The amount of polystyrene added is 0.4 wt% SiC for the 5 vol% SiC in decahydronapthalene. The deposition was done for 60 seconds and the DC voltage applied was +4kV........................................................................................39 7-7 The amount of LP1 and polystyrene(PS) added are 0.4 wt% SiC for the 5 vol% SiC in decahydronapthalene. The depos ition time was 60 seconds and the DC voltage applied was +4kV........................................................................................39 8-1 The variation of shear st ress with shear rate for a 0.4 wt% LP1 stabilized slurry with 5 vol% SiC in decahydronapthalene................................................................40 8-2 The variation of shear stress with visc osity for a 0.4 wt% LP1 stabilized slurry with 5 vol% SiC in decahydronapthalene................................................................41 8-3 Variation of relative visc osity with solids lo ading of SiC in decahydronapthalene with 0.3 wt% SiC, being the polybutadiene (PB) amount.......................................42 8-4 Variation of relative visc osity with solids lo ading of SiC in decahydronapthalene with 0.4 wt% SiC, being the LP1 amount................................................................43 8-5 Variation of relative visc osity with solids lo ading of SiC in decahydronapthalene with 0.4 wt% SiC, being the polystyrene (PS) amount...........................................44 8-6 Variation of relative visc osity with solids lo ading of SiC in decahydronapthalene with 0.4 wt% SiC, being the LP1 and pol ystyrene (PS) amou nts and 0.3 wt% SiC the polybutadiene (PB) amount................................................................................45 9-1 Variation of optical density with vol tage for a LP1 slurry without charge controlling agents and with a deposition time of 120 seconds.................................47 9-2 Variation of optical density with voltage for a LP1 slurry with charge controlling agent 7 and a deposition time of 60 seconds............................................................48 9-3 Variation of optical density with voltage for a LP1 slurry with charge controlling agents and with a depos ition time of 120 seconds...................................................49

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x 9-4 Variation of optical density with volta ge for polystyrene slurry without charge controlling agents and a depos ition time of 60 seconds...........................................50 9-5 Variation of optical density with volta ge for polystyrene slurry with charge controlling agent 7 and a deposition time of 60 seconds.........................................51 9-6 Variation of optical density with volta ge for polystyrene slurry with charge controlling agent 7 and a deposition time of 120 seconds.......................................52 9-7 Variance of optical density with voltage for 5 vol% SiC in decalin with 0.4 wt% SiC being the LP1 and polystyrene (PS) amounts...................................................53 10-1 Variation of optical density with time for a LP1 slurry without charge controlling agents and a deposition voltage of +2kV.................................................................55 10-2 Variation of optical density with time for a LP1 slurry without charge controlling agents and a deposition voltage of +4kV.................................................................55 10-3 Variation of optical density with time for a LP1 slurry with charge controlling agent 7 and a deposition voltage of +2kV................................................................56 10-4 Variation of optical density with time for a polystyrene sl urry without charge controlling agents and a depos ition voltage of +4kV...............................................57 10-5 Variation of optical density with time for a polystyrene slurry with charge controlling agent 7 and a depos ition voltage of +2kV.............................................57 10-6 Variation of optical density with time for a polystyrene slurry with charge controlling agent 7 and a depos ition voltage of +4kV.............................................58 10-7 The variation of optical density with time for a 5 vol% SiC in decahydronapthalene with 0.4 wt% SiC be ing the LP1 and polystyrene (PS) amounts....................................................................................................................59 11-1 SEM of the electrophoretic deposit formed from th e 5 vol% SiC suspension in decahydronapthalene with polystyrene....................................................................62 11-2 SEM of the electrophoretic deposit formed from th e 5 vol% SiC suspension in decahydronapthalene with polystyrene and the charge controlling agent 7.............62 11-3 SEM of the electrophoretic deposit formed from th e 5 vol% SiC suspension in decahydronapthalene with LP1 polymer..................................................................63 11-4 SEM of the electrophoretic deposit formed from th e 5 vol% SiC suspension in decahydronapthalene with LP1 polymer and the charge controlling agent 7..........64

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xi 11-5 Digital camera picture of the steel electrode after it was dipped into the 5 vol% SiC in decahydronapthalene with LP1 polymer suspension and kept for 60 seconds without the app lication of a voltage...........................................................65 11-6 Digital camera picture of the steel electrode after it was dipped into the 5 vol% SiC in decahydronapthalene suspension with LP1 polymer and kept for 60 seconds with the application of a voltage of +4kV..................................................66 11-7 Digital camera picture of the steel electrode after it was dipped into the 5 vol% SiC in decahydronapthalene suspension with the polystyrene polymer and kept for 60 seconds without the application of a voltage.................................................66 11-8 Digital camera picture of the steel electrode after it was dipped into the 5 vol% SiC in decahydronapthalene suspension with LP1 polymer and kept for 60 seconds with the application of +4kV and for another 60 seconds with the application of -4kV...................................................................................................68

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xii Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science DEVELOPMENT OF AN ALPHA SILICON CARBIDE BASED LIQUID TONER FOR ELECTRO-PHOTOGRAPHIC SOLID FREEFORM FABRICATION By NAVIN JOSE MANJOORAN May 2003 Chair: Wolfgang. M. Sigmund Major Department: Materials Science and Engineering Most industrial ceramic processing applicati ons require slurries that can be easily poured with the highest solids loading. This helps in making the final cast have a good packing uniformity and reduces the sintering shrinkage. Rheological studies are carried out with alpha silicon carbide slurries in a non-polar media using polystyrene, polybutadiene and LP1 dispersants. The experi mental data were fit into the KriegerDougherty equation to find out the maximum so lids loading and collo idal properties of the slurry. A novel solid freeform method, “Electro-phot ographic Solid Freef orm Fabrication” (ESFF), needs specific qualities for solid ( powder) and liquid (slurr y) toner (electronic ink). The development of a liquid toner, st udy of its flow behavi or and electrophoretic tests confirming that the toner could be us ed for ESFF are carried out and the data analyzed.

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1 CHAPTER 1 INTRODUCTION A novel Solid Freeform Fabrication (SFF) method, referred to as Electrophotographic Solid Freeform Fabrication (ESFF) needs specific qualities for a toner material (solid or liquid). By using a liqui d toner we can deal with sub-micron size powders, which would help in improving the resolution of the prot otype obtained. Here, we deal with preparing a liqui d toner and carrying out tests to show that the liquid toner can be used for the solid freeform fabricati on process. A liquid toner consists of submicron sized particles dispersed in a nonpolar solvent, with polymers acting as dispersants and charge contro lling agents maintaining the charge. Rheology studies were done to find the maximum solids loading that can be obtained for the slurries with polystyrene, LP1 and polybutadiene. The mode ls were fit to the Krieger-Dougherty equation. Electrophoretic tests were done to st udy the variance of optical density with voltage and time. Chapter 2 deals with an introduction to so lid freeform fabricat ion. A brief history, how the process works, the advantages and the applications of SFF are described here. The later part of the chapter deals with a novel SFF technique refe rred to as electrophotographic solid freeform fabrication. In chapter 3, a discussion is based on basic theories and concepts that exist in colloida l processing, mainly, the various stabilization methods and coagulation. The dependence of viscosity on packing fraction, the KriegerDougherty equation and basic concepts on rheo logy are discussed in chapter 4.Chapter 5 deals with the methodology for the materials selection. How and why the specific

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2 materials were chosen for the experiment s are explained. In chapter 6, the various characterizations on the raw materials ta ken are explained. The methodology for the experiments and the equipments used for the various experiments are also mentioned here. Chapter 7 deals with determining the amount of polymer needed to completely cover the silicon carbide particle and to dete rmine the amount of charge controlling agent needed to get the required electrophoretic deposition. The dependence of relative viscosity on solids loading of the slurry, the KriegerD ougherty fit curves and the determination of the maximum solids loading fo r the slurry are concentrated in chapter 8. Chapter 9 deals with the study of the variance of optical densit y with voltage and to find out the best voltage region to carry out the electrophoretic depositions at. In chapter 10, the concentration is on the study of the vari ance of optical density with time for the slurries having polystyrene as the polymer and those having LP1 as the polymer. The analysis of the electrophoret ic deposition is seen in Chap ter 11. The pictures of the deposition are also present here. Chapter 12 gi ves a brief conclusion to the results of the experiments.

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3 CHAPTER 2 GENERAL THEORIES AND CONCEPTS IN SOLID FREEFORM FABRICATION History The thought of making three-dimensional obj ects, without the use of any tooling methods have interested scientists for ma ny years [1]. Technique’s using a specific hardening feature by the laser beam, were available in the early eighties [2]. Hull and Charles [3] patented the stereolithography apparatus in 1986. By this process threedimensional plastic parts could be created directly from Comput er Aided Design (CAD) data. From then on many Solid Freeform Fabrication (SFF) techniques have been developed. What Is SFF? Solid Freeform Fabrication (SFF) is a method to fabricate custom threedimensional objects with desired properties from computer data [4, 5] This is basically a layer-by-layer manufacturing method of threedimensional objects. Due to this layer-bylayer building approac h, quicker and cheaper production of prototypes could be made. First, the solid model of the part to be manu factured is created in CAD software. This is then exported to the SFF process via a software interface [4]. The software interface is java or java2 and the program used is the solid slicer. The SFF process deposits various materials layer by layer in the shape of the cro ss-section of the solid to create the part. A simplified flow diagram is shown in figure 2-1.

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4 Figure 2-1.Block diagram of the principle of the solid freefor m fabrication (SFF) technique The automation for the entire process is also possible. In theory, since the prototypes can be produced very fast the solid freeform fabrication is also referred to as Rapid Prototyping (RP). Solid freeform fabrication methods can be classified on the basis of the raw material used, lighting of photopolymers, and by the application range for which it is used [2]. The earliest form of SFF was ster eolithography [3, 5]. Ster eolithography uses an Ultra Violet (UV) laser (generally a heliumcadmium laser) to create successive cross sections of three-dimensional objects within a vat of liquid photopolymer. This technique makes use of photo reactive polymers, those that react with UV light. When UV light strikes the photo reactive polymer resin, it gets solidified. Thus, in th is manner a layer of the three-dimensional model could be form ed. The process is continued by either Computer Aided Design, 3D Model Solid Freeform Fabrication Process 3-D Object Additional Materials

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5 lowering the object into the vat of the polymer or by spreading a new layer on the object in order to make the next and subsequent la yers form the solid part. A schematic diagram of the stereolithography prototyping system stated by Hu ll and Charles [2] is shown in figure 2-2. The parts that are built using st ereolithography are durab le, but fragile. The stereo lithographic machine is accurate with building parts co ntaining intricate details and complex shapes. 3D systems of Valencia, CA, since 1988 is the industry leader in selling RP machines particularly those usin g stereo lithographic techniques. Computer Control UV Light 3D Parts Resin Z Figure 2-2.The stereo lithographic machine [2] SFF has been associated with manufacturing environments, where it is used for the rapid production of visual models, low r un tooling and functional objects [6]. The additive nature of SFF techniques, offers gr eat promise for producing objects with unique material combinations and geometries, wh ich could not be attained by traditional methods and are different from most m achining processes (milling, drilling, grinding, etc), as these are subtractive processes that re move material from a solid block. So, it can be used in diverse fields as aerospace, elec tronics, architecture, biomedical engineering and archeology [6]. SFF allows designers to quickly create tangibl e prototypes of their

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6 designs rather than two-dimensional pictures These help in making less expensive and excellent visual aids for communicating ideas wi th co-workers or customers. It can also be used for design testing. For small producti on runs and complicated objects, SFF is the best process available. The time required to build the prototype depends on the size and complexity of the object. The time saving al lows manufacturers to bring products to the market faster and more economically [6]. Electro-photographic Solid Freeform Fabric ation (ESFF) is a novel solid freeform fabrication technique. It uses the electro-photography techniqu e to deposit particles layerby-layer on a specially designed pl atform. [1, 7, 8] (Figure 2-3) Figure 2-3.The electro-phot ographic solid freeform fabr ication (ESFF) machine [8] During the electro-photography process, th e particles are picked up by a charged surface and deposited on an oppositely charge d surface. Therefore, it is important to know the characteristics, especi ally the charging characteristic s of the particles in this process. Kumar [1] has designe d a test-bed, ESFF machine (Figure 2-4), which deposits

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7 the particles in the required regions, layer-bylayer, on a numerically controlled two-axis platform. Figure 2-4.A schematic of the electro-photogr aphic solid freeform fabrication (ESFF) machine [8] A heating and compacting system is used to fuse each layer of particles deposited. Figure 2-5 shows a schematic representation of how the ESFF process works. The photoconductor drum is charged with the help of a charging roller using direct contact charging. The laser image projector make s the image on the photoconductor drum by removing the charge from the drum at the required regions. From the image developer Figure 2-5.A sketch showing the principle of the electro-photographic solid freeform fabrication (ESFF) machine [8]

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8 the particles are attracted to the magnetic development drum, by applying a high voltage on the drum. The particles then get transferred to the photoc onductor drum at the regions required because of their opposite polarity. The developed image is then transferred onto the build platform with the help of an elec tric field and then permanently fixed by fusing. The photoconductor surface needs to be cleaned using physical or electrical methods, before the process is repeated to get the three-dimensional object. Of late, there has been a great demand worldwide for electro-photography based full color printing devices for both Small Of fice and Home Office (SOHO) and for the heavy volume commercial application [ 9, 10, 11, and 12]. The printing “toner” (electronic ink) can be either in the powder form (solid toner) or the sub-micron sized toner particles can be suspended in a dielectr ic liquid (liquid toner). There has been an increasing demand for a high quality short run printing and the liquid development process using a liquid toner can meet this demand well because with this we can achieve high resolution, good image quality and a bett er packing uniformity [13]. Thus, liquid toners are important and there is the need to develop a liquid toner for the ESFF process.

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9 CHAPTER 3 BASIC THEORIES AND CONCEPTS IN COLLOIDAL PROCESSING A colloid consists of two phases [14]. On e of the phases, referred to as the dispersion medium is generally a solid, liquid or a gas and the other, the finely dispersed particulate phase, is either a gas, liquid or a solid. It is seen that compared to powder consolidation methods, using colloidal susp ensions, leads to a much better packing uniformity in the green body for sub-micron si zed particles. This helps in achieving superior micro-structural properties during sintering. The use of a high solids loading slurry, reduces the shrinkage due to sintering, during the compaction process. Moreover, the sinterability is also better using a high so lids loading slurry. However, the difficulty lies in making a colloidal suspension with th e highest possible solids loading and a low enough viscosity so that it can be poured. [14] For colloidal suspensions, to give th e best packing uniformity, the suspension prepared must be stable. When particles ar e close together, the attractive van der Waals forces tend to coagulate the particles. To a void coagulation, various stabilization methods can be used which are explained below. A st able high solids loading colloidal suspension can be consolidated to a densely packed structure. Stabilization Methods for Colloids For particles in a liquid dispersing medium attractive van der Waals forces tend to flocculate the particles. To avoid flocculati on or coagulation of pa rticles, a reduction in the attractive forces is needed and the techniques used to achieve this are based on introduction of repulsive for ces [14]. The repulsion between particles, based on the

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10 electrostatic charges on the particles is te rmed as electrostatic stabilization. The stabilization mechanism is termed as polym eric stabilization, when the repulsion is produced by polymer molecules, adsorbed or chemically attached, onto the particle surfaces or existing freely in the solution. When repulsion is a consequence of the combination of electrostatic and polymeric stabilization mechanisms it is termed as electrosteric stabilization [14]. Electrostatic Stabilization In electrostatic stabilizati on, the repulsion is not between the charged particles. A diffuse electrical double layer of charge is produced between the particles and this interaction formed between the diffused doubl e layers formed is the cause for the repulsion. For a particle covered by a diffuse doubl e layer, the shear slippage occurs at a distance from the surface and the potential at this shear slippage is termed as the zeta potential. The zeta potential is the potentia l at the surface of the electrokinetic unit, moving through the liquid medium, as determ ined from the measured electrophoretic mobility [14,15]. For ceramic particles dispersed in a solu tion the main process by which they can acquire a surface charge is by the adsorption of ions from the solution. The surfaces of oxide particles are normally hydrated in water. The adsorption of H+ ions produces a positive charge on the oxide surface and similarly the adsorption of the OHions produces a negative charge on the oxide surface. At some intermediate pH, the adsorption of H+ ions will balance that of the OHions. This intermediate pH is called as the Point of Zero Charge (PZC)[14]. At this point, th e particle surface is effectively neutral. It is observed that the measurement of th e surface potential is difficult, as some finite ionic dimensions, could approach only up to a certain distance of the interface. This

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11 led to the stern layer effect. Th e stern layer effect states th at the double layer consists of three regions. The outermost layer is called the ‘diffuse double layer.’ The layer formed due to the adsorption and which lies adjacent to the particles interface is called the ‘inner Helmholtz layer.’ Figure 3-1.The double layer consisting of the three regions [15] The layer where the counter ions were arrange d at a distance form the interface is called as the ‘outer Helmholtz layer’. It is easier to measure the poten tial at a small distance form the particle surface, that is, at the surface of the ster n layer and this potential is 0 sDiffuse double laye r Shear plane Stern plane Distance

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12 referred to as the zeta potent ial. The pH where the charge on the stern layer is zero, rather the zeta potential is zero, is refe rred to as the Iso-Electric Point (IEP). Double Layer Repulsion It is seen that for colloidal particles, wh en two particles come closer together their double layers start to overlap. If the particle s carry the same charge, repulsion is seen after their double layers overlap resulting from inter-penetration of the two diffuse layers. This repulsion prevents further movement of the particles closer together and is believed to be the reason for the stability of the su spension. The universally accepted theory for the interaction between electr ical double layers is the DL VO theory (after Derjaguin, Landau, Verwey and Overbeek) [14, 16]. DLVO Theory Named after Derjaguin, Landau, Verwey and Overbeek, this theory explains the interactive forces acting between the electric double layers. The theory states that the total interaction energy is the sum of the at tractive potential en ergy and the repulsive potential energy. VT = VA + VR [3.1] The electric double layer stabilization is seen when the double layers of similarly charged particles approach each other and th e repulsive forces between them are large enough to overcome the van der Waals forces of attraction. Polymeric Stabilization This is the stabilization of the colloidal particles by organic polymer molecules. It can be accomplished by either steric stabiliz ation or depletion st abilization. When the stabilization mechanism is achieved by polymer molecules adsorbed or attached to the colloidal particle, the mechan ism is referred to as steric stabilization. When the

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13 stabilization is achieved by polymer molecule s in the free solution it is termed as depletion stabilization [14]. Figure 3-2.The variation of potential energy between two particles in a liquid medium due to van der Waals attraction and electric double layer repulsion [15,16] Electrosteric Stabilization Electrosteric stabilization requires the pr esence of both the adsorbed polymers and the double layer repulsion a combination of the electrostatic and ster ic forces. This can be achieved by using a charged particle and a neutral polymer, by using a neutral particle and a charged polymer or by using a charge d particle and a ch arged polymer [14].

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14 Coagulation The potential barrier decides the stability of a suspension. In most colloids the particles remain suspended only when the ener gy barrier is greater than kT. In other cases, it is seen that the particles tend to adhe re to each other. If this process is reversible it is termed as flocculation and if it is irreversible it is term ed as coagulation. A coagulate is defined as a set of partic les in suspension held togeth er by attractive van der Waals forces [14, 15].

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15 CHAPTER 4 BASIC CONCEPTS AND THEORIES IN UNDERSTANDING THE RHEOLOGICAL PROPERTIES FOR PARTICULATE SUSPENSIONS Rheology is the study of deformation and fl ow of matter. As th e stability of the dispersion is dependent on the final structural outcome of the consolidated solid, it is important to understand and know the rheologi cal properties of the colloidal suspension. A good colloidal suspension is one that has a high solids loading and a low viscosity. The high solids loading helps obtain a high pack ing density during the compaction process. The viscosity of the suspension should be lo w enough so that it can be poured easily [16, 17, 18]. Importance of Rheological properties The most important property used to descri be the flow of a liquid is its viscosity. By carefully analyzing the viscosity we can find out the maximum solids loading that can be achieved for the suspension. This helps in making suspensions with high packing densities during compaction a nd reduces the shrinkage. The viscosity is defined as = \ [4.1] where, is the viscosity, is the shear stress and is the shear rate. From the variation of viscosity with shear rate of the suspension we can know if the liquid shows a Newtonian beha vior or not. For Newtonian liquids, the viscosity is independent of the shear rate of the suspen sion. However, for most of the suspensions generally used, such as polymer suspensions or colloidal suspen sions the viscosity

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16 changes with shear rate of the suspension and are therefore termed as non-Newtonian liquids. Therefore in these cases the visc osity will be a function of shear rate. Depending on how the viscosity varies with shear rate we can have different kinds of liquids. If the viscosity of the suspension de creases with shear rate it is called as shear thinning or pseudoplastic liquid a nd if the viscosity increases with the shear rate it is called as shear thickening or dilatancy. We have the thixotropic behavior when the viscosity depends not only on th e shear rate but also on time. Figure 4-1.The variation of shear stress and viscosity with shear rate. A. newtonian Liquid, B. dilatant liquid a nd C. pseudoplastic liquid Solids Loading We consider the particles to be hard s pheres, for better understanding of the effect of the concentration of the particles. This means we discard the presence of charged

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17 electrical double layers or adsorbed polymers According to Einstein, the increase in the viscosity is caused by the increase in the soli ds loading as shown in the equation below = 0 ( 1 + 2.5 ) [4.3] where, is the viscosity of the suspension, 0 is the viscosity of the liquid medium, is the volume fraction of the particles. A more generalized equation is = 0 ( 1 + k1 ) [4.4] where, k1 is the Einstein’s coefficient, which is 2.5 for hard spheres. However this equation particularly deals wi th dilute suspensions (when there is no interaction between the particles). For con centrated suspensions, the equation becomes more complex and is given by, = 0 ( 1 + k1 + k22 + k33 + k44+ ...) [4.5] Generally the viscosity is expres sed as the relative viscosity ( r ) and is the ratio of the viscosity of the suspension ( ) to the viscosity of the liquid medium ( 0). As more and more particles are added into the solution, there is an increase in the solids loading and finally at a certain solids loading the viscosity reaches infinity. This limiting value is called the maximum solids loading ( m). At the maximum volume fraction, the particles in the sl urry are so close together that their average separation distance is almost zero and this makes th eir flow impossible [18,19]. The maximum solids loading is around 0.65 for hard sphere s and maybe around 0.4 0.5 for colloidal suspensions in which the interaction between the particles are si gnificant. Depending on the slurry that is prepared we can have variations in the maximum solids loading

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18 For mono-size spheres, the Krieger and Dougherty equation e xplained [14, 16] below can be used to calculate the maximum solids loading which is given by mm r ] [1 [4.6] where [ ] is the intrinsic viscosity and m is the maximum solids loading. Particle Size Analysis The particle size and size di stribution does have an imp act on the viscosity of the colloidal suspension. It is seen that th e Krieger Dougherty fit works only when the particles are mono dispersed. Wh en the particles are poly-disp ersed it is seen that the maximum solids loading is different compared to the mono-dispersed particles as the smaller particles can occupy the voids betw een the larger particles. For mono sized particles the viscosity reaches a maximum valu e at a lower solids loading. Thixotrophic behavior or lowering of the maximum solids loading is seen when the majority of the particles are of the smaller size range. This happens as the particles have a large specific surface area for the solvent and dispersant to bi nd to. Dilatancy, due to the obstruction of flow of particles leads to a lowering of th e solids loading in the suspensions having a majority of particles of the larger size. Polymer Adsorbed Layers The adsorption (chemical bonding) of polymer layers onto the su rface of particles can result in a better stabilizat ion of the colloidal suspension. If the polymers are organic in nature, steric stabilization is seen. If the polymers are ionizable, the stabilization mechanism is a combination of the steric and the electrostatic methodselectrosteric stabilization. The adsorbed la yer of the polymer should be such that they can overcome the van der Waals forces of a ttraction and thereby prevent the adherence of the particles.

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19 The polymer additions of the amount of 0.4-0.5 % of the weight of the particles can help achieve fairly low viscosities at high solids loading [14].

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20 CHAPTER 5 METHODOLOGY FOR LIQUID TONER MATERIAL SELECTION In liquid development systems, non-aqueous dispersions consisting of sub-micron sized particles stabilized in an adsorbed la yer of polymer and char ge control agents in aliphatic hydrocarbons are used as toners [20]. Solvent–Selection Methodology As, ISOPAR (ISOPARaffinic hydrocarbon – highly branched alkanes with 7-15 carbon atoms), the solvent used in most indus trial applications for the development for the liquid toner, is not well defi ned, a solvent with similar pr operties as of ISOPAR and a clearly defined structure was sele cted. Thus, decahydronapthalene (C10H18) was used as the solvent [18, 21, and 22]. The properties c onsidered were a high flash point (135F for decahydronapthalene), non-polar nature, nonconductivity, chemical in ertness, relatively non-viscous nature and volatility. Decahydrona pthalene meets the majority of these requirements. The chemical structure for decah ydronapthalene is given in figure 5-1. Ceramic Particles–Se lection Methodology Silicon Carbide (SiC), sub-micron sized particles were used, as they are an important ceramic for structural and electri cal applications, because of their excellent mechanical and electrical properties at hi gh temperatures [18, 19]. Sub-micron sized particles were made use of to produce very high-resolution images [13]. Silicon carbide has been used as an industrial product for mo re than hundred years. It can be used for a broad range of applications like high temperature semiconductors, medical, biomaterials and light weighthigh strengt h structural materials.

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21 Figure 5-1.The chemical structures fo r trans and cis decahydronapthalene. Dispersing Agent–Selection Methodology The adsorbed layer of the polymer should be such that they can overcome the van der Waals forces of attraction and thereby pr event the adherence between the particles. To find suitable dispersing agents for the SiC and C10H18 system, the refractive indices and dielectric constants for silicon carbide and decahydronapthalene were substituted in transDecalin cis Decalin

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22 [5.1] the Tabor-Winterton equation mentioned below and the Hamaker constant was calculated [17]. For the SiC and C10H18 system the refractive indices are 2.649 [23] and 1.475 [24] respectively and the dielectric constants ar e 9.71 [25] and 2.196 [26] respectively at 298K. Using these values in the Tabor Wi nterton Approximation (TWA), the Hamaker constant was calculated to be 2.233*10-19J for the SiC–C10H18 system [16]. A graph, for sphere-sphere interactions, at 298K, with th e Hamaker constant of the system, showing the variation of separation distance of SiC particles with respect to the van der Waals interaction energy was plot [figure 5-2]. The figure 5-2 shows an increase in the ma gnitude of the van der Waals interaction energy as the particle separation distance de creases. The increase in the van der Waals interaction energy can be seen to start when the separation distance is 40 nm. So, if we can keep the particles 40 nm apart, by using a polymer, we could avoid the coagulation of the particles due to van der Waals interac tion. Using the solubility parameter handbook, the solubility parameters for pol ymers [polybutadiene (18.0 (MPa)0.5) and polystyrene (18.6 (MPa)0.5) ] having similar solubility para meter values with that of C10H18 (18.0 (MPa)0.5 ) were chosen [27]. Now, using the formu la for the radius of gyration(r) given

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23 SPHERE/SPHERE INTERACTIONS -14 -12 -10 -8 -6 -4 -2 0 0.0100.0200.0300.0400.0500.0600.0 Separation Distance (nm)Vanderwalls Interaction Energy (kT) SPHERE/SPHERE INTERACTIONS Temperature : 293 K Particle radius:0.55 m van der Waals attraction Hamaker constant:2.23*10-19 J below the approximate molecular weights required for these polymers were calculated [14]. Figure 5-2.Separation distance (nm) for SiC pa rticles with the van der Waals interaction energy (kT) in the sphere-sphere inter action mode. The Hamaker constant for the calculation was taken to be 2. 23*10-19J and the temperature was 298K r2 = c n l2 [ 5.2 ] where, ‘l’ is the segment length, ‘c’ is a constant factor and ‘n’ is the number of segments. The average molecular weights required for polystyrene and polybutadiene were calculated to be in the order of 105 and 103, respectively. Actual solubility tests showed that polybutadiene and polystyrene were soluble in the non-pol ar solvent. Thus, polybutadiene, polystyrene and for compar ison, Hypermer LP1 (High performance polymeran industrially used polymer) were chosen.

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24 Charge Controlling Agents–Selection Methodology In industrial systems, particle charge c ontrolling agents are added to control the magnitude and sign of the surface charge of th e particles [18, 28, 29, and 30]. Therefore, CCA7, an industrially used ne gative charging agent, was us ed to provide the charge.

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25 CHAPTER 6 RAW MATERIALS CHARACTERIZATI ON AND EXPERIMENTAL TECHNIQUES 6H-alpha silicon carbide (Grade UF15, H.C.Starck, Canada), cis-trans decahydronapthalene (Aldrich), polystyrene (Aldrich), polybutadiene (Aldrich), LP1 (Uniqema, Belgium) and charge controlli ng agent 7 (Avecia-Inc) were the starting materials. The average molecular weights fo r polystyrene, polybutadiene and LP1 are ~230000, ~ 5000 and ~ 6000 respectively. The Silicon Carbide (SiC) and Charge Controlling Agent 7 (CCA7), particle si zes, were measured with the Brookhaven instruments – Zeta plus particle sizing and were found to yield a d50 of 0.520.02 m and 0.420.02 m respectively. The surface area of SiC, measured by BET (AREAMETER II) N2 adsorption is 15m/g (H.C. Starck). Po lystyrene, polybutadiene and LP1 are used as dispersants for the different experiment s and their amounts are based on the weight percent of the dry SiC powder. Table 6-1.Raw materials us ed for the experiments S.No Material Company D50, Mw BET surface area 1 6H-alphasilicon carbide H.C.Starck, Canada D50 of 0.520.02 m, 15m/g 2 Cis-trans decahydronapthale ne Aldrich 99+% purity 3 Polystyrene Aldrich Mw ~ 230,000 4 Polybutadiene Aldrich Mw ~ 5,000 5 LP1 Uniqema, Belgium Mw ~ 6,000 6 Charge controlling agent 7 Avecia-Inc D50 of 0.420.02 m Scanning Electron Microscopy (SEM ) The SEM imaging was carried out using the JEOL JSM6330F. The JEOL 6330 is a cold field emission scanning electron micr oscope. The cold field emission has the

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26 advantage of high brightness (large current density) and small beam diameter (high resolution) at low accelerating voltages to allow imaging of soft polymeric materials without causing damage to the sample. Resolu tion of the instrument is around 1.5nm depending on the sample. The instrument ha s an energy dispersive X-ray spectrometer (EDS) for elemental analysis. Figure 6-1.SEM picture of the 6H-a lphasilicon carbide (UF Grade 15) The SEM image for SiC was taken at 10,000X magnification with a working distance of 14.6mm. The figure 6-1 shows that the particles are mainly spherical and are more or less of the same size and shape. The SEM picture for the CCA7 was taken at 8,000X magnification with a working distance of 16.2mm. The figur e 6-2 shows that th e particles are mainly rod shaped.

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27 Figure 6-2.SEM picture of the charge controlling agent (CCA7) Energy Dispersive x-ray Spectrometry (EDS) The EDS was carried out using the JEOL JSM6330F SEM. The instrument has an energy dispersive X-ray spectrometer (EDS) for elemental analysis which was used. The EDS of CCA7 shows that the negative charge controlling agent is mainly a chromium complex (figure 6-3). Figure 6-3.EDS of the charge controlling agent 7 (CCA7)

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28 Nuclear Magnetic Resonance Spectroscopy (NMR) Nuclear magnetic resonance spectroscopy ma kes use of the spin of the media to study physical, chemical, and biological pr operties of matter. Nuclear magnetic resonance is a phenomenon which occurs when the nuclei of certain atoms are immersed in a static magnetic field and exposed to a second oscillating magnetic field. Dependent upon whether they possess the property call ed spin, some nuclei experience this phenomenon, and others do not. The carbon (13C) NMR and the proton (1H) NMR for the LP1 polymer were taken. The NMR for the LP1 polymer shows that the polymer consists of single bonded carbon and hydrogen Figure 6-4.The carbon (13C) NMR for the LP1 polymer

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29 Figure 6-5.The proton (1H) NMR for the LP1 polymer Planetary Ball Mill The pulverisette 5” laboratory planetary ball mill with a maximum speed of 350rpm was used initially for th e lower solids loading slurries Zirconia balls were used as the milling media and the mill jars are made of Alumina. But, due to losses in the slurry suspension by using the ball m ill, the misonix sonicator was used.

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30 Misonix Sonicator 3000 For high solids loading slurries, the mi sonix sonicator 3000 ultrasonic horn was used for the suspension preparation. The ge nerator provides high vol tage energy pulses at 20 kHz and takes care of the changes in th e load conditions such as viscosity and temperature. A titanium disruptor horn transmits and focuses oscillations of the piezoelectric crystals and causes radiati on of energy which under a phenomenon called “cavitation” (formation and destruction of th e microscopic vapor bubbles that the sound waves generate) produces the shearing and tearing action necessary for the slurry formation. Suspension Preparation Measured amounts of decahydronapthalene and the polymer (polystyrene or polybutadiene or LP1) are taken in a beaker and placed on a hot stirrer till the polymer dissolves in the carrier. This is followed by the addition of measured amounts of CCA7 and the product is placed in a misonix soni cator 3000 ultrasonic horn for 60 minutes. SiC is then added. The product is then placed in misonix sonicator 3000 ultrasonic precursor for 120 minutes. The suspension is thus prep ared. This procedure is used for making slurries to determine the optimum amounts of the polymer, charge controlling agent required and for making slurries wi th different solids loading Rheometer Viscosity measurements were performe d using a modular compact rheometer (MCR 300, Paar Physica) with a concentric cyli nder system using the US200 universal software. The inner cylinder diameter is 27 mm. The temperature unit features peltier heating.

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31 Viscosity Measurements The shear flow measurements are operated at 298K. The shear rate changes from 0.001 to 1000 s-1. The temperature cont rol unit is TEZ150P, whic h features peltier heating. The slurry is pre-sheared at 800s-1 for 60 seconds. The slurry is then kept stationary for 10 seconds to equilibrate. Th en the measurements are carried out. The relative viscosity is the ratio of the viscosity of the suspension to the viscosity of decahydronapthalene, at the same temperature [15]. Optical Density Measurement Equipment Setup The voltage measurements during the elec trophoretic deposition are done using the DC voltage source (1-5 kV, Matsusada). A glass container holds the slurry. A steel electrode acts as the cathode and another as the anode. The gap betw een the electrodes is 6 cm. One of the electrodes is grounded a nd on the other a developing bias voltage is applied. The optical density is the ratio of the deposited mass to the surface area and this gives information on the darkness of the pr int [13, 31, 32 and 33]. The application of voltage leads to the deposition of SiC particle s on the electrode. By measuring the optical density for different voltages and time, graphs are plot showing the variation of optical density with voltage and time

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32 Figure 6-6.Flowchart for the suspension preparation DECALIN HEAT ADD CCA7 SONICATOR ADD SiC ULTRASONIC HORN RHEOLOGICAL MEASUREMENTS POLYMER

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33 CHAPTER 7 EFFECT OF POLYMER ADSORPTI ON ON RHEOLOGY AND SOLIDS LOADING OF THE SUSPENSION Determination of the Optimum Amount of Polymer The amount of the polymer added to the su spension must be just enough so that it covers the SiC surface completely. The additi on of excess may cause an increase in the viscosity and if less than the required amount is added, the repulsive forces are not strong enough to overcome the van der Waals forces of attraction. When ther e is the addition of the optimum amount of the polymer, the repu lsive barrier potential is high enough to overcome the attractive potential [14, 15 and 17]. The optimum amount is the lowest point on the graph plot betw een the weight percent of dispersant and viscosity. Optimum Amount of Polystyrene The viscosity measurements were carried out for different weight percent of polystyrene in 5 vol% SiC with decahydronapthale ne as the solvent. The shear rate taken for the measurement is 161s-1. It is assumed that the lowest point in the figure 7-1, when there is the complete coverage of the silicon carbide particles, is at 0.4 wt% polystyrene. Thus, for all further experiments the amount of polystyrene added was fixed at this value. Optimum Amount of LP1 Viscosity measurements were carried out for different weight percent of LP1 in 5 vol% SiC with decahydronapthalene as the solvent. The shear rate taken for the measurement is 99.9s-1. It is assumed that the lowest point in the figure 7-2, when there is

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34 the complete coverage of the silicon carbide particles, is at 0.4 wt% LP1. Thus, for all further experiments the amount of LP 1 added was fixed at this value. Wt % Dispersant Vs Viscosity (Pa.s)0 0.005 0.01 0.015 0.02 0.025 0.03 00.20.40.60.81 Wt % dispersantViscosity (Pa.s) PS Shear rate 161 1/s Figure 7-1.Optimum amount of polystyrene re quired for complete coverage of the SiC surface. The shear rate is 161s-1. Optimum Amount of Polybutadiene The viscosity measurements were carried out for the different weight percent of polybutadiene in 5 vol% SiC with decahydronapt halene as the solvent. The shear rate taken for the measurement is 99.9s-1. It is assumed that the lowe st point on the figure 7-3, when there is the complete coverage of th e silicon carbide partic les, is at 0.4 wt% polybutadiene. Thus, for all further experime nts the amount of polybutadiene added was fixed at this value.

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35 Wt % Dispersant Vs Viscosity (Pa.s)0 0.002 0.004 0.006 0.008 0.01 0.012 0.014 00.20.40.60.81 Wt % dispersantViscosity (Pa.s) LP1 Shear rate 99.9 1/s Figure 7-2.Optimum amount of LP1 required fo r complete coverage of the SiC surface. The shear rate is 99.9s-1. Wt % Dispersant Vs Viscosity (Pa.s)0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 00.20.40.60.81 Wt % dispersantViscosity (Pa.s) PB Shear rate 99.9 1/s Figure 7-3.Optimum amount of po lybutadiene required for comp lete coverage of the SiC surface. The shear rate is 99.9s-1.

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36 Comparison of the Optimum Amounts of Dispersants The variation of viscosity with diffe rent weight percent of polystyrene, polybutadiene and LP1 in 5 vol% SiC with d ecahydronapthalene as the solvent is shown in figure 7-4. It can be seen that the optim um amount for polystyre ne, polybutadiene and LP1 are 0.4, 0.3 and 0.4 wt% SiC respectivel y. Therefore, with the addition of the optimum amount of the polymer, the repul sive barrier potential is high enough to overcome the attractive potential and the comp lete coverage of the SiC particles is obtained. Wt % Dispersant Vs Viscosity (Pa.s)0 0.005 0.01 0.015 0.02 0.025 0.03 00.10.20.30.40.50.60.70.80.91Wt % dispersantViscosity (Pa.s) A : LP1 Shear rate 99.9 1/s B : PS Shear rate 161 1/s C : PB Shear rate 99.9 1/s Figure 7-4.5 vol% SiC in decahydronapthalene with varying amounts of the dispersants polystyrene(PS), polybutadiene(PB) and LP1 used. Determination of the Optimum Amo unt of Charge Controlling Agent In industrial systems, the particle ch arging agents are added to control the magnitude and the sign of the charge, for better dispersability and to adjust the

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37 triboelectrically generated charge of the t oner [18]. The optimum amount of the charge controlling agent added to the suspension is the minimum amo unt that must be added to get the highest amount of uniform deposition. Optimum Amount of CCA7 in the LP1 suspension In figure 7-5, there is an increase in th e optical density with the addition of CCA7 for the slurry with the LP1 polymer and af ter further addition of CCA7 this value decreases. It is seen, that the maximum opti cal density and therefor e the optimum amount of CCA7 is seen when the amount of CCA7 is 0.1 times the amount of polymer added. 5 vol% SiC in decahydronapthalene was used for the experiments. The time (sec) mentioned for which the deposition was done was 60 seconds and the DC voltage applied was +4kV. The amount of LP1 polymer added was 0.4 wt% SiC. Optimum amount of CCA7 in the Polystyrene Suspension In the figure 7-6 there is a decrease in the optical density with the addition of CCA7 for the slurry with polys tyrene and after further a ddition of CCA7 this value increases. It is seen, that the maximum opti cal density and therefor e the optimum amount of CCA7 is seen when the amount of CCA7 is 0.1 times the amount of polymer added. 5 vol% SiC in decahydronapthalene was used for the experiments. The time (sec) mentioned for which the deposition was done was 60 seconds and the DC voltage applied was +4kV. The amount of polystyrene (PS) added was 0.4 wt% SiC. Therefore, for polystyrene, the optimum amount of CCA7 is taken as 0.1 times the amount of the polymer, as in this case the best depositi on and maximum optical density is obtained.

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38 Log value of Amount of CCA7 Vs Optical density (gcm2 )0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 -3.5-3-2.5-2-1.5-1-0.50Log (Amt of CCA7 wrt Amt of polymer added)Optical Density ( gcm2 ) A: LP1, 4 kV, 60 Sec Figure 7-5.The amount of LP1 added is 0.4 wt% SiC for the 5 vol% SiC in decahydronapthalene. The deposition was done for 60 seconds and the DC voltage applied was +4kV. Comparison of the Optimum Amounts of CCA From figure 7-7, the optimu m amount of CCA7 is taken as 0.1 times the amount of the LP1 polymer or polystyrene added as in this case we get the best deposition and the maximum optical density. The optimum amount of the charge contro lling agent added to the suspension is the minimum amount that mu st be added to get the highest amount of uniform deposition and the maximum optical density.

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39 Log value of Amount of CCA7 Vs Optical density (gcm2 )0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 -3.5-3-2.5-2-1.5-1-0.50Log (Amt of CCA7 wrt Amt of polymer added)Optical Density ( gcm2 ) A : PS, 4 kV, 60 sec Figure 7-6.The amount of polystyrene added is 0.4 wt% SiC for the 5 vol% SiC in decahydronapthalene. The deposition was done for 60 seconds and the DC voltage applied was +4kV. Log value of Amount of CCA7 Vs Optical density (gcm2 )0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 -3.5-3-2.5-2-1.5-1-0.50Log ( Amount of CCA7 with respect to amount of polymer added )Optical Density ( gcm2 ) A : PS, 4 kV, 60 sec B : LP1, 4kV, 60 sec Figure 7-7.The amount of LP1 and polystyrene(PS) added are 0.4 wt% SiC for the 5 vol% SiC in decahydronapthalene. The deposition time was 60 seconds and the DC voltage applied was +4kV

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40 CHAPTER 8 EFFECT OF RELATIVE VISCOSITY ON SOLIDS LOADING OF THE NON POLAR SILICON CARBIDE SUSPENSION The viscosity of the slurry depends on th e solids loading and this value reaches infinity at the maximum volume fraction ( m). The maximum volume fraction depends on the particle size and the particle shape. At the maximum volume fraction, the particles in the slurry are so close together that thei r average separation distance is almost zero and this makes their flow impossible [14,16]. The experimental points have been fit to the modified Krieger-Dougherty [16] equation. For a SiC slurry in decahydronapthalene, th e variation of shear rate with shear stress shows a shear thinni ng behavior (figure 8-1). 0.1 1 10 100 0.1110100100010000 Shear Rate (s-1)Shear Stress (Pa) Figure 8-1.The variation of shear stress with shear rate for a 0.4 wt% LP1 stabilized slurry with 5 vol% SiC in decahydronapthalene.

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41 It is seen that with an incr ease in the shear rate there is also an increase in the shear stress following the curve for the shear thinning behavior.The variation of shear rate with viscosity, for a SiC slurry in decahydronapt halene, shows a shear thinning behavior (figure 8-2). It is seen that with an increase in the shear ra te there is a decrease in the viscosity of the slurry. 0.01 0.1 1 10 0.1110100100010000 Shear Rate (s-1)Viscosity (Pa.s) Figure 8-2.The variation of shear stress with vi scosity for a 0.4 wt% LP1 stabilized slurry with 5 vol% SiC in decahydronapthalene. Relative Viscosity on Solids Loading for the Polybutadiene Stabilized Suspension From the figure 8-3, the graph between the volume fractions of silicon carbide with respect to the relative viscosity the maximum solids loading, m, for the polybutadiene suspension is found to be 0.69 ( =5.24). The higher m value illustrates that the packing

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42 behavior is high in this case. The viscosity measurements were taken at a shear rate of 99.9s-1. Figure 8-3.Variation of relative viscosity with solids loading of SiC in decahydronapthalene with 0.3 wt% Si C, being the polybutadiene (PB) amount. The amount of CCA7 added was 0.1 times the amount of polymer added to the slurry. Relative Viscosity on Solids Loading De pendence for the LP1 Stabilized Suspension From the figure 8-4, the graph between the volume fractions of silicon carbide with respect to the relative viscosity the maximum solids loading, m, for the LP1 suspension is found to be 0.55 [ =5.4 ]. The higher m value illustrates that the packing behavior is high in this case. The viscosity measurements were taken at a shear rate of 99.9s-1.

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43 Figure 8-4.Variation of relative viscosity with solids loading of SiC in decahydronapthalene with 0.4 wt% SiC, being the LP1 amount. The amount of CCA7 added was 0.1 times the amount of polymer added to the slurry. Solids Loading Dependence on Relative Vi scosity for the Polystyrene Stabilized Suspension From the figure 8-5, the graph between the volume fraction of silicon carbide with respect to the relative viscosity the maximum solids loading, m for the polystyrene suspension is found to be 0.22 ( =12.8 ). The lower m value illustrates that the packing behavior is poor in this case. The viscosity measurements were taken at a shear rate of 99.9s-1.

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44 Figure 8-5.Variation of relative viscosity with solids loading of SiC in decahydronapthalene with 0.4 wt% SiC, being the polystyrene (PS) amount. The amount of CCA7 added was 0.1 tim es the amount of polymer added to the slurry. Comparison of the Stabilization Methods The best fit of the experi mental data shows that m is drastically lower for the suspension with polystyrene (0.22 [ =12.8]) compared to the LP1 suspension (0.55 [ =5.4]) or the polybutadiene suspension (0.69 [ =5.24]). We see that there is an evident difference in the order of magnit ude of the packing behaviour. The lower m value illustrates that the packing behavior is poor in these cas es. Therefore, the polystyrene suspension will have a lower pack ing behavior than the polybutadiene and LP1 polymer suspensions.

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45 Figure 8-6.Variation of relative viscosity with solids loading of SiC in decahydronapthalene with 0.4 wt% SiC, being the LP1 and polystyrene (PS) amounts and 0.3 wt% SiC the polybutadiene (PB) amount.The amount of CCA7 added was 0.1 times the amount of polymer added to the slurry

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46 CHAPTER 9 EFFECT OF OPTICAL DENSIT Y VARIANCE WITH VOLTAGE The voltage measurements during the elec trophoretic deposition are done using the DC voltage source (1-5 kV, Matsusada). The opt ical density is the ratio of the deposited mass to the surface area and this gives inform ation on the darkness of the print [13, 28, 32, and 33]. The application of voltage lead s to the deposition of SiC particles on the electrode. By measuring the optical density fo r different voltages and times, the variation of optical density with voltage were obtained Optical Density Variance with Voltage for LP1 The variation of voltage with opt ical density, for a 5 vol% SiC in decahydronapthalene suspension, with LP1 polym er used as the dispersant are seen in figures 9-1, 9-2 and 9-3. From the trend line in the figures it can be seen that initially the optical density increases rapidl y with voltage and after a whil e it stabilizes and there is not too much of an increment in the optical density with increase in voltage. This point usually seen at +4kV gave the best uniform deposition and so can be considered as the best region to have the e xperiments carried out at. For figure 9-1, the deposition was done for 120 seconds with no charge controlling agent. The optical density increases rapidly in itially and then stabilizes as shown by the trend line. It is seen that at voltages below 4kV, the deposition formed is not uniform. The lowest voltage at which the uniform depos ition is seen to be achieved at was +4kV. Hence +4kV was used for the experiments as the best voltage to work with.

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47 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 010002000300040005000 Voltage ( V ) Optical Density (g/ cm2) Figure 9-1.Variation of optical density with voltage for a LP1 slurry without charge controlling agents and with a deposition time of 120 seconds. For figure 9-2, the deposition time was 60 seconds with the charge controlling agent in the slurry. The optical density in creases rapidly initially and then if we extrapolate the graph it stabilizes as shown by the trend line. It is seen that at voltages below +4kV, the deposition formed is not uniform. The lowest voltage at which the uniform deposition is seen to be achieved was +4kV.

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48 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0100020003000400050006000 Voltage ( V ) Optical Density (g/ cm2) Figure 9-2.Variation of optical density with voltage for a LP1 slurry with charge controlling agent 7 and a de position time of 60 seconds. For figure 9-3, the deposition was done for 120 seconds with the charge controlling agent. The optical density increases rapidly in itially and then stabi lizes at around +4kV as shown by the trend line. The lowest voltage at which the uniform depos ition is seen to be achieved was +4kV. Hence +4kV was used for the experiments as the best voltage to work with.

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49 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0100020003000400050006000 Voltage ( V ) Optical Density (g/ cm2) Figure 9-3.Variation of optical density with voltage for a LP1 slurry with charge controlling agents and with a deposition time of 120 seconds. Optical Density Variance with Voltage for Polystyrene Figures 9-4, 9-5 and 9-6 show the variation of voltage with optical density, for a 5 vol% SiC in decahydronapthalene suspension, wi th polystyrene used as the dispersant. From the trend line in the figures it can be s een that initially the optical density increases rapidly with voltage and afte r a while it stabilizes and th ere is not too much of an increment in the optical density with increase in voltage. This point usually seen at +4kV gave the best uniform deposition and so can be considered as the best region in which for conducting the experiments. For figure 9-4, the deposition was done for 60 seconds and no charge controlling agent was used. The lowest voltage at whic h the uniform deposition is seen to be

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50 achieved was +4kV. Hence +4kV was used for the experiments as the best voltage to work with. 0 0.01 0.02 0.03 0.04 0.05 0.06 0100020003000400050006000 Voltage ( V ) Optical Density (g/ cm2) Figure 9-4.Variation of optical density with vol tage for polystyrene slurry without charge controlling agents and a deposition time of 60 seconds. For figure 9-5, the deposition was done for 60 seconds with the charge controlling agent. The optical density increases rapidly in itially and then stabilizes as shown by the trend line. It is seen that at voltages below +3kV, the deposition formed is not uniform. The lowest voltage at which the uniform de position is seen to be achieved was +4kV. Hence +4kV was used for the experiments as the best voltage to work with.

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51 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0100020003000400050006000 Voltage ( V ) Optical Density (g/ cm2) Figure 9-5.Variation of optical density with voltage for polystyrene slurry with charge controlling agent 7 and a de position time of 60 seconds. For figure 9-6, the deposition was done for 120 seconds with the charge controlling agent. The optical density increases initially and then stabilizes. It is seen that at voltages below 4kV, the deposition formed is not uni form. The lowest voltage at which the uniform deposition is seen to be achieve d was +4kV. Hence +4kV was used for the experiments as the best voltage to work with. Comparison of Optical Density Variance with Voltage for LP1 and Polystyrene Figure 9-7 shows the optical density variation of the LP 1 and polystyrene slurries with and without the addition of CCA7 at diffe rent voltages and times. It can be inferred from the data that LP1 slurries are better than polystyrene slurries as they have a much higher optical density at the same voltage. Th erefore, better liquid toners can be made using the LP1 slurries.

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52 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0100020003000400050006000 Voltage ( V ) Optical Density (g/ cm2) Figure 9-6.Variation of optical density with voltage for polystyrene slurry with charge controlling agent 7 and a de position time of 120 seconds. It can also be inferred from th e figure that a higher optical density was obtained with the presence of the charge controlling agent (c omparing the trend lines for C and D with A and B or comparing the trend line for H with F) It is also seen that, the greater the time of deposition, the greater was the optical density (comparing the trend lines for C with D and A with B). Also, there was deposition on th e steel electrode with the LP1 slurries by the application of a high positive voltage and there was no deposition on the application of a negative voltage. A positive voltage was applied and a layer of SiC was made to adhere to the electrode and by reversing the voltage this laye r could be removed. This property of the LP1 slurries can be used for electro-photographic solid freeform fabrication, where the steel electrode would be the photocond uctor drum for the printer. However in the case of the polys tyrene slurries the applica tion of either a high positive

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53 voltage or a high negative voltage led to th e deposition of SiC pa rticles onto the steel electrode. Therefore, these polys tyrene slurries cannot be used as a liquid toner as they do not completely follow the adhesion-non adhe sion behavior with the application of alternating positive and negative voltages. A DC voltage of +4kV is good for the process as a good uniform deposition was seen to take place at this voltage. Voltage ( V ) Vs Optical Density ( g/ cm2 )0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0100020003000400050006000Volta g e ( V ) Optical Density (g/ cm2) E : PS, 2 min,W -CCA TREND LINE FOR C TREND LINE FOR D TREND LINE FOR A TREND LINE FOR B TREND LINE FOR H TREND LINE FOR F A: LP1, 2 min, W -CCA B : LP1, 1 min,W -CCA C : LP1, 2 min, CCA D : LP1, 1 min, CCA F : PS, 1 min,W -CCA G : PS, 2 min, CCA H : PS, 1 min, CCA Figure 9-7.Variance of optical density with voltage for 5 vol% SiC in decalin with 0.4 wt% SiC being the LP1 and polystyrene (PS) amounts.CCA, stands for the slurries in which 0.1 times the amounts of polymer of CCA7 was added to the slurry. W-CCA stands for those slurri es in which CCA7 was not added. The time (min) mentioned are the time for which the deposition was done.

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54 CHAPTER 10 EFFECT OF OPTICAL DENSITY VARIANCE WITH TIME The voltage measurements during the elec trophoretic deposition are done using the DC voltage source (1-5 kV, Matsusada). The opt ical density is the ratio of the deposited mass to the surface area and this gives inform ation on the darkness of the print [13, 31, 32 and 33]. The application of voltage leads to the deposition of SiC particles on the electrode. By measuring the optical density fo r different times and voltages, the variation of optical density with time were plot. Optical Density Variance with Time for LP1 The variation of time with optical density, for a 5 vol% SiC in decahydronapthalene suspension, with LP1 polym er used as the dispersant are shown in figures 10-1, 10-2 and 10-3. From the trend line in the figures it can be seen that there is a linear increase in optical de nsity increases with time. For figure 10-1, the applied voltage was + 2kV and no charge controlling agent was used. The optical density increases linear ly with time as shown by the trend line. For figure 10-2, the applied voltage was + 4kV with no charge controlling agent. The variation of optical density with time is linear. Therefore with an increase in time there is a higher optical density For figure 10-3, the applied voltage was + 2kV with the charge controlling agent being in the slurry. A linear relationship is seen with the optical density and time as shown by the trend line.

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55 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 050100150200250300350 Time (sec)Optical Density (g/ cm2) Figure 10-1.Variation of optical density with time for a LP1 slurry without charge controlling agents and a de position voltage of +2kV. 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 050100150200250300350 Time (sec)Optical Density (g/ cm2) Figure 10-2.Variation of optical density with time for a LP1 slurry without charge controlling agents and a de position voltage of +4kV.

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56 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 050100150200250300350 Time (sec)Optical Density (g/ cm2) Figure 10-3.Variation of optical density w ith time for a LP1 slurry with charge controlling agent 7 and a de position voltage of +2kV. Optical Density Variance with Time for Polystyrene Figures 10-4, 10-5 and 10-6 show the varia tion of time with optical density for a 5 vol% SiC in decahydronapthalene suspension, wi th LP1 polymer used as the dispersant. From the trend line in the figures it can be s een that the optical density increases with an increase in time. For figure 10-4, the applied voltage was + 4kV with no charge controlling agent. A linear relationship between optical density a nd time is seen as shown by the trend line. Therefore with an increase in time a better optical density can be obtained. For figure 10-5, the applied voltage was + 2kV with the charge controlling agent being in the slurry. The optical density incr eases linearly with time as shown by the trend line.

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57 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 050100150200250300350 Time (sec)Optical Density (g/ cm2) Figure 10-4.Variation of optical density with ti me for a polystyrene sl urry without charge controlling agents and a de position voltage of +4kV. 0 0.01 0.02 0.03 0.04 0.05 0.06 050100150200250300350 Time (sec)Optical Density (g/ cm2) Figure 10-5.Variation of optical density with time for a polystyrene slurry with charge controlling agent 7 and a de position voltage of +2kV.

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58 For figure 10-6, the applied voltage was + 4kV with the charge controlling agent. The trend line shows that a in crease in optical density is obtained with time. Therefore with longer duration for th e deposition a higher optical density can be obtained. 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 050100150200250300350 Time (sec)Optical Density (g/ cm2) Figure 10-6.Variation of optical density with time for a polystyrene slurry with charge controlling agent 7 and a de position voltage of +4kV. Comparison of Optical Density Variance with Time for LP1 and Polystyrene Figure 10-7, shows the optical density varia tion of the LP1 and polystyrene slurries with and without the addition of CCA7 at diffe rent times and voltages. It can be inferred from the data that LP1 slurries are better than polystyrene slurries as they have a much higher optical density as compar ed to polystyrene slurry for the same time of deposition. Therefore, better liquid toners can be made us ing the LP1 slurries. It can also be seen, from the figure, that a higher voltage gave a higher optical density (comparing the trend lines for E and F) and similarly the presen ce of CCA7 increases the optical density

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59 (comparing B with C and G with E). It’s also seen that with an increase in time there is a better optical density and this follows a linear relationship. For liquid toner applications a higher optical density in a mini mum time of deposition is needed. So it can be seen that the LP1 slurry can be used as a liquid toner. It was seen, during the experiments that the uniformity in the deposition on the electrode occurred at voltages around +4kV. So most of the experiments were carried out at +4kV. Time (sec) Vs Optical Density (g/cm2)0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 050100150200250300350Time (sec)Optical Density (g/ cm2) A : LP1, 2kV, W-CCA B : LP1, 4kV, W-CCA C : LP1, 2kV, CCA D : LP1, 4kV, CCA E : PS, 2kV, W-CCA F : PS, 4kV, W-CCA G : PS, 2kV, CCA H : PS, 4kV, CCA TREND LINE FOR D TREND LINE FOR C TREND LINE FOR B TREND LINE FOR G TREND LINE FOR F TREND LINE FOR E Figure 10-7.The variation of optical density with time for a 5 vol% SiC in decahydronapthalene with 0.4 wt% SiC being the LP1 and polystyrene (PS) amounts. CCA, stands for the slurries in which 0.1 times the amounts of polymer of CCA7 was added to the slurry W-CCA stands for those slurries in which CCA7 was not added. The voltage s mentioned are the DC voltages for which the deposition was done.

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60 CHAPTER 11 ANALYSIS OF THE ELECTROPHORETIC DEPOSITION For the electro-photographic solid freefor m application, electrophoretic adhesionnon adhesion tests were carried out to find out the best volume fraction to work with. For the adhesion-non adhesion tests, the steel electrode was dipped into slurries with LP1, polybutadiene and polystyrene as dispersants and at different solids loading of 5, 10, 15, 20, 30, 40, 50 and 60 vol% SiC. The aim was to work with the slurry, into which if the electrode was dipped and kept for a certain pe riod of time (60 seconds) and taken out, did not have any SiC particles deposited. The l ong term application bei ng that the electrode could be used as the photoconductor drum in the printer. It was found that at lower volume fractions this adhesion-non adhesion beha vior was seen better and for slurries with polystyrene and LP1, a perfect example of this was seen at 5 vol% SiC. So, further experiments were carried out with 5 vol% Si C. Polybutadiene slurries did not make a favorable response to the adhesion-non adhesi on tests and so were not considered for making a liquid toner. Since LP1 and polystyrene satisfied the firs t set of experiments. The next test was to place the electrode in the slurry and to apply a voltage on the electrode for 60 seconds. The electrode was then taken out of the suspension. The aim of the experiment was to see if a layer of silicon carbide was deposited on the electrode or not. It was seen that both polystyrene and LP1 satisfied these tests. The final experiment was to place the el ectrode in the slurry, apply a voltage, reverse the voltage and see if most of the deposition could be taken off from the

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61 electrode. For the LP1 slurries there wa s deposition on the steel electrode by the application of a high positive voltage and th ere was no deposition on the application of a negative voltage. A positive voltage was applie d and a layer of SiC was made to adhere to the electrode and by reversing the voltage this layer could be removed. This property of the LP1 slurries can be used for electro -photographic solid freefor m fabrication, where the steel electrode would be the photoconductor drum for the printer. However in the case of the polystyrene slurries the application of either a high positiv e voltage or a high negative voltage led to the deposition of SiC particles onto the steel electrode. Therefore, these polystyrene slurries cannot be used as a liquid toner as they don’t completely follow the adhesion-non adhesion behavior with th e application of alternating positive and negative voltages. A DC voltage of +4kV is good for the process as a good uniform deposition was seen to ta ke place at this voltage. Scanning Electron Microscope Images Polystyrene Samples The SEM images of the deposited laye r with the suspension of 5vol% SiC in decahydronapthalene with polystyrene is seen in figure 11-1. A voltage of +4kV was applied for 60 seconds. The SEM image was taken at a magnification of 20,000X with a working distance of 13.3mm. The SEM images of the deposited layers with the suspension of 5vol% SiC in decahydronapthalene with polystyrene and the ch arge controlling agent, CCA7 is seen in figure 11-2. A voltage +4kV was applied fo r 60 seconds. The SEM image was taken at a magnification of 20,000X and a wo rking distance of 14.3mm.

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62 Figure 11-1.SEM of the electr ophoretic deposit formed from the 5 vol% SiC suspension in decahydronapthalene with polystyrene. Figure 11-2.SEM of the electr ophoretic deposit formed from the 5 vol% SiC suspension in decahydronapthalene with polystyrene and the char ge controlling agent 7.

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63 LP1 Samples The SEM images of the deposited laye r with the suspension of 5vol% SiC in decahydronapthalene with LP1 is seen in figur e 11-3. A voltage of +4kV was applied for 60 seconds. The SEM image was taken at a magnification of 10,000X with a working distance of 15.5mm. Figure 11-3.SEM of the electr ophoretic deposit formed from the 5 vol% SiC suspension in decahydronapthalene with LP1 polymer. The SEM image of the deposited layers with the suspension of 5vol% SiC in decahydronapthalene with LP1 and the charge controlling agent, CCA7 is seen in figure

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64 11-4. A voltage of +4kV was applied for 60 seconds. The SEM image was taken at a magnification of 10,000X with a working distance of 13.4mm. Figure 11-4.SEM of the electr ophoretic deposit formed from the 5 vol% SiC suspension in decahydronapthalene with LP1 polymer and the charge controlling agent 7. Digital Camera Pictures Digital camera pictur es of the electrophor etic deposition done were taken and are seen in figures 11-5, 11-6, 11-7, 11-8 and 119. Figure 11-5 is a pi cture taken after the steel electrode was dipped into a 5vol% SiC in decahydronapthalene with the LP1 polymer suspension for 60 seconds. There was no voltage applied. We see that there is no layer formed on the electrode. Therefore, this sl urry satisfied the first test A slurry into

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65 which if the electrode was dipped and kept fo r a certain time and then taken out did not have any SiC particles adhered to it. Figure 11-5.Digital camera picture of the stee l electrode after it was dipped into the 5 vol% SiC in decahydronapthalene with LP1 polymer suspension and kept for 60 seconds without the a pplication of a voltage. Figure 11-6 is a digital camera picture of a steel electrode after it was dipped in the 5 vol% SiC in decahydronapthalene with the LP1 polymer suspension for 60 seconds. The voltage applied was +4kV. We see that there is a uniform layer formed on the electrode. Therefore, this slurry satisfied the second test A slurry into which if the electrode was dipped and kept for a certain ti me, at a particular vol tage and then taken out had SiC particles adhered to it. Figure 11-7 shows a picture taken after the steel electrode was dipped into a 5 vol% SiC in decahydronapthalene with the polys tyrene polymer suspension for 60 seconds. There was no voltage applied. We see that there is no layer formed on the electrode.

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66 Therefore, this slurry satisfied the first test – A slurry into which if the electrode was dipped and kept for a certain time and then taken out did not have any SiC particles adhered to it. Figure 11-6.Digital camera picture of the stee l electrode after it was dipped into the 5 vol% SiC in decahydronapthalene suspen sion with LP1 polymer and kept for 60 seconds with the applica tion of a voltage of +4kV Figure 11-7.Digital camera picture of the stee l electrode after it was dipped into the 5 vol% SiC in decahydronapthalene suspen sion with the polystyrene polymer and kept for 60 seconds without the application of a voltage

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67 Figure 11-8 and 11-9 are digital camera pictur es of the steel el ectrode after it was dipped in the 5 vol% SiC in decahydronaptha lene suspension with the LP1 polymer. A voltage of +4kV was applied for 60 seconds a nd then the voltage was reversed to -4kV for 60 seconds. We see that there is hardly any of the SiC deposit left on the electrode. Therefore, this slurry satisfied the third test A slurry into which if the electrode was dipped and kept for a certain time, for a partic ular voltage and then reversing the voltage and keeping it for the same amount of time and when taken out had no SiC particles adhered to it.

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68 Figure 11-8 and 11-9.Digital camera picture of the steel electrode af ter it was dipped into the 5 vol% SiC in decahydronapthalene suspension with LP1 polymer and kept for 60 seconds with the applicati on of +4kV and for another 60 seconds with the application of -4kV.

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69 CHAPTER 12 CONCLUSION The optimum amounts for polystyrene, polybutadiene and LP1 polymers are 0.4, 0.3 and 0.4 wt% SiC respectively. The ma ximum optical density and therefore the optimum amount of Charge Controlling Agen t (CCA7) is when the amount of CCA7 is 0.1 times the amount of polystyrene or LP1 a dded to the slurry. All slurries are shear thinning. The dependence of relative viscos ity on solids loading is different for the slurries with LP1, polybutadiene or polystyrene as the poly mer. There is an order of magnitude difference in the maximum solids loading between these slurries. The maximum solids loading attainable ( m ) using the KriegerDoughe rty fit equation, for the polystyrene slurry was 0.22 [ =12.8]. For the LP1 slurry the maximum solids loading ( m ) was 0.55 [ =5.4] and for the polybutadiene slurry ( m ) was 0.69 [ =5.24]). Lower solids loading indicate poor particle pa cking. Therefore, the packing density will be higher for the polybutadiene slurries as co mpared to the LP1 and polystyrene slurries. At lower volume fractions [5 vol % SiC] the electrophoretic adhesive-non adhesive behavior was better for slurri es with polystyrene and LP1. Polybutadiene sl urries did not make a favorable response to the adhesivenon adhesive tests and so were considered “not good” for making a liquid toner. Bette r deposition can be made using the LP1 slurries as they have a much higher optical de nsity as compared to polystyrene slurry at the same voltage. Polystyrene slurries cannot be used as a liquid toner as they don’t completely follow the adhesivenon adhesive be havior with the application of alternating positive and negative voltages. A +4kV DC vo ltage was found to be sufficient for the

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70 electrophoretic deposition proces s. There is a large increase in the optical density with the addition of the CCA7 in the sl urry. A linear dependence of optical density on deposition time was established experimentally.

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71 LIST OF REFERENCES [1] V. Kumar, Solid Freeform Fabricate on Using Power Deposition, U.S. Patent 6,066,285 (2000) [2] D. Kochan, Solid Freeform Manufacturing, Advanced Rapid Pr ototyping, Elsevier, Amsterdam (1993) [3] E. Hull, W. Charles, Apparatus For Pr oduction Of ThreeDimensional Objects By Stereolithography, US Patent 4,575,330 (1986) [4] G. Sumit, Rapid Prototyping, Master’s Thesis, University of Florida, (2001) [5] V. Kumar, S. Rajagopalan, M. Cutkoshy and D. Dutta, Representation and Processing of Heterogeneous Objects for Solid Freeform Fabrication, IFIP WG5.2 Geometric Modeling Workshop, Tokyo (1998) [6] A. Kumar, Rapid Prototyping, http:/ /caec.me.ufl.edu/~akumar/research/esff.htm (accessed April 2002) [7] V. Kumar, H. Zhang, Electro-photo graphic Powder Deposition for Freeform Fabrication, 10th Solid Freeform Fabrication Proceedings, pp. 639-646 (1999) [8] A. Kumar, A. Dutta, Investigation of an Electro-photography Based Rapid Prototyping Technology, accepted for publ ication Rapid Prototyping Journal (2003) [9] J. Chang, A.J. Kelly, J.M. Cowley, Handbook of Electrostatic Processes, Marcel Dekker, Inc. New York (1995) [10] L. Schein, Electro-photography and De velopment Physics, Springer series in electro physics 14, Springer Verlag, New York (1992) [11] R. Baur, H. Macholdt, E. Michael, C. Zeh, Clariant Gmbh, BU-Pigments, European Conference on Pigments, Frankfurt, Germany (1998) [12] L. de Schamphelaere, Short Run Digital Color Printing, IS&T 11th International Congress, Hilton Head, SC (1995)

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72 [13] S. Matsumoto, K. Satou, J. Matsuno, A. Sasaki, T. Akasaki and K. Kamio, Mechanism of Liquid Development Usi ng Highly Concentrated Liquid Toner, IS&T 11th International Conference on Digita l Printing Technologies,Berkeley, California, (2002) [14] M. N. Rahaman, Ceramic Processing a nd Sintering, Marcel Dekker Inc, New York (1995) [15] K. Sunita, Impact of Electric Doubl e Layer and Electrost eric Stabilization Mechanisms on Solids Loading of Aqueous Alumina Slurries, Master’s thesis, University of Florida (2002) [16] W. Sigmund, N. Bell, L. Bergstrom, Novel Powder Processing Methods For Advanced Ceramics, Journal of American Ceramics Society, 83[7]1557-74 (2000) [17] Y. Yang, W. Sigmund, Preparation, Ch aracterization and Gelation of Temperature Induced Forming (TIF) Alumina Slurries Journal of Materials Synthesis and Processing, 9[2], (2001) [18] J. Thomas, Particle Charging In Non Polar Media, http://www.laser.unisa.edu.au/ nonpolar.htm (accessed April 2002) [19] R. Li, Temperature Induced Direct Cas ting of SiC, Dissertation an der Universitt Stuttgart (2001) [20] M. Omodani, W. Lee, Y. Takahashi, Present Status of Liquid Toner Development Technology and the Problems to be Solv ed, IS&T Internat ional Conference on Digital Printing Technologies, Jacksonville, Florida (1998) [21 ] Y. Otsubo, Y. Suda, Electro-Rheological Toners for Electrop hotography, Journal of Colloid and Interfacial Science, 253,224-230 (2002) [22] G. Gibson, J. Larson, Liquid Toner Printing: Technology an d Applications,Xerox Corporation, Columbus, Ohio (2002) [23] J. F. Kelly, Polytypism in Silicon Carbide, http://img.cryst.bbk.ac.uk/www/kelly/litera turesicweb.shtml (accessed April 2003) [24] C. Crystals, I ndex Matching Fluids, http://www.clevelandcrystals.com/ nmatch.shtml (accessed April 2002) [25] Materials Handbook, Dielectric Cons tant for SiC, http://www.ncsr.csciva.com/materials/sic.asp (accessed April 2002) [26] Materials Datasheet, Dielectric Constant for Decalin, http://www.magnetrol.com.br/diel etrico.pdf (accessed April 2002)

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73 [27] E. Grulke, Solubility Parameter Values Chemical and Materials Engineering Data Tables, University of Kentuc ky, Lexington, Kentucky (1996) [28] R. Baur, H. Macholdt, E. Michel, Streaming Current Charge Versus Trio Charge, Electrostatics, Proceedings of the 10th International conference, New York, 285288 (1999) [29] K. Birkett, P. Gregory, Metal Comple x Dyes as Charge Control Agents, Dyes and Pigments, Journal of Rapid Pr ototyping, 7[5] 341-350 (1986) [30] R. Baur, H. Macholdt, E. Kiss, M. Kohno, Charge Control Agents for Triboelectric (Friction) Charging, Journal of Electrostatics, 30, 213-222 (1993) [31] T. Takashi, N. Hosono, J. Kanbe T. Toyona, Introduction to Photographic Processes, Photography Science Engineering, 26, 254 (1982) [32] R. W. Gundlach, Screened Donor fo r Touchdown Development, U.S. Patent 4,556,013 (1985) [33] L. Walkup, Developer for Electros tatic Images, U.S. Patent 2,618,551 (1952)

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74 BIOGRAPHICAL SKETCH Navin was born on the 4th of July 1979, in Cochin, I ndia–the queen of the Arabian Sea. Being an outstanding student al l though his academic career, he received scholarships for his entire schooling. He is an amazing tennis play er and was ranked in the top hundred in singles and doubles in me n’s tennis in India (1997). He has even participated and won prizes (1990-95) at the na tional level in enterpri se class sailing and water-skiing. His first steps towards an engineering car eer came in May 1997 with his admission into the prestigious Regional Engineering Co llege (now called the National Institute of Technology), Warangal, Andhra Pradesh, India– the oldest of the NITs. A consistently high academic performance got him the “Naval Foundation” scholarship for his entire undergraduate program in Metallu rgical Engineering. He gr aduated from NIT, Warangal with the “Alumni Association Gold Medal,” for being the best out going student and allrounder and also the “Sri Kabadi Subalu Silver Medal,” for being the best outgoing sportsperson among the students graduating in the year 2001. The first student from NIT Warangal since it was founded in 1959 to wi n two of these prestigious medals. After graduation, a decision had to be made between joining Mahindra British Telecomm (MBT), Pune, India, as a software engineer or to go in for higher studies. A graduate research assistants hip with Dr Wolfgang Sigm und in Materials Science and Engineering at the University of Florida, Gainesville, made the decision easier. Ever since, Navin has been here at Gainesville and will be graduating with a Master of Science

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75 degree in May 2003. At Gainesville, he has continued to involve himself with the international community and is presently the vice president of the Indian Student Association (ISA) on campus, the largest ISA in the United States. He is also the Indian representative to the Student Government (SG) and the Volunteers of International Students Association (VISA) on campus.


Permanent Link: http://ufdc.ufl.edu/UFE0000741/00001

Material Information

Title: Development of An Alpha Silicon Carbide Based Liquid Toner for Electro-Photographic Solid Freeform Fabrication
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0000741:00001

Permanent Link: http://ufdc.ufl.edu/UFE0000741/00001

Material Information

Title: Development of An Alpha Silicon Carbide Based Liquid Toner for Electro-Photographic Solid Freeform Fabrication
Physical Description: Mixed Material
Copyright Date: 2008

Record Information

Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
System ID: UFE0000741:00001


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DEVELOPMENT OF AN ALPHA SILICON CARBIDE BASED LIQUID TONER
FOR ELECTRO-PHOTOGRAPHIC SOLID FREEFORM FABRICATION















By

NAVIN JOSE MANJOORAN


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA


2003

































This document is dedicated to my father, my mother and my brother Neil.















ACKNOWLEDGEMENTS

This paper is the fruit of the enduring support, love and cooperation of my mother

Mrs. Grace Jose and father Mr. Jose Manjooran. Although they are thousands of miles

away, they have been unshakable pillars of support, helping me fight and win every

battle. Their faith in my abilities has been my strength and their visions my inspiration.

All those words of wisdom have been my driving force through all those hard times. No

words said can express how indebted I am to them for what I am today and for what I

shall accomplish in the future.

I would also like to thank my brother, Neil, for being there and helping to keep me

going on and on. Joy uncle, Elizabeth aunty, Varkeychan uncle, Minna aunty,

Thomachan uncle, Lizy aunty, Tony uncle and Devi aunty have given me the strength

and the endurance to complete what I started and the motivation to excel in it. They have

been my "safety net" throughout my graduate education.

Dr. Sigmund, my advisor, my teacher, my supervisor and my mentor, taught me

more than I ever hoped to learn here at graduate school. His work has been my

inspiration. This work has been a product of his patience and endurance. He has inspired

me to be a better researcher and also a better person. He understood my problems and has

helped me to succeed in spite of them. My success is and will be a reflection of his

outstanding abilities as a teacher. I hope to do my best in whatever task I undertake and

always strive for perfection, as a tribute to him. Nothing short of this will be adequate to

express my gratitude to him.









I would like to thank Dr. Zaman for all the support he has given me through the

entire project. His support and cooperation all through the project helped me immensely.

I am grateful to Dr. Butt for agreeing to be on my committee and giving me valuable

suggestions. I would also like to thank Dr. Kumar, for constantly guiding me with my

experiments and for always being ready to help.

Words cannot express my gratitude for my friends here in Gainesville, for always

being there when I needed them most. Abhishek, Agam, Ajay, Amit, Amol, Amrita,

Anagha, Bharti, Bullet, Devraj, Dhruv, Gargi, Jairaj, Jason, Javid, Jayashree, Joanne,

Joyti, Kunal, Lal, Nova, Nyla, Priya, Sajan, Sidd, Sudeep, Sandeep, Sandy, Seemanth,

Seethu, Shruti, Sonali, Soumya, Teena, Thrity, Unnat, Vijayram, Vivek and the entire

graduating class of 2003. I would also like to thank all the students in our research group

"Dr. Sigmund's Research Group" for being the greatest group ever-helpful, supportive

and understanding. I would also like to thank the entire Materials Science and

Engineering Department for making this possible.
















TABLE OF CONTENTS
page

A C K N O W L E D G E M E N T S ......... .................................................................................. iii

LIST OF FIGU RE S ........................................ ............ .............. .. viii

ABSTRACT ........ .............. ............. .. ...... .......... .......... xii

CHAPTER

1 INTRODUCTION ............... ................. ........... ................. ... ..... 1

2 GENERAL THEORIES AND CONCEPTS IN SOLID FREEFORM
FA B R IC A TIO N ................. .................................... .. ........ ....... .. .. ..3

H isto ry ............................................................................ . 3
W hat Is SF F ? ......................................................................... . 3

3 BASIC THEORIES AND CONCEPTS IN COLLOIDAL PROCESSING.................9

Stabilization M ethods for C olloids.................................................... .....................9
E lectrostatic Stabilization ............................................................... .................. 10
D ouble L ayer R epulsion ......................................................................... ... ... 12
D L V O T h eory ................................................... ................ 12
P olym eric Stabilization ............................................... ............................ 12
Electrosteric Stabilization..................... ...... ............................. 13
C oagulation ........................................................................................................14

4 BASIC CONCEPTS AND THEORIES IN UNDERSTANDING THE
THEOLOGICAL PROPERTIES FOR PARTICULATE SUSPENSIONS ...............15

Im portance of Rheological properties ............................................. ............... 15
S olid s L loading ...................................... .............................. ................. 16
Particle Size A analysis ............................................ ............ .. ............ 18
Polym er A dsorbed Layers ................................................ .............................. 18

5 METHODOLOGY FOR LIQUID TONER MATERIAL SELECTION...................20

Solvent-Selection M methodology ......... .. ............ .................. .....................20
Ceramic Particles-Selection Methodology............................. .......................20
Dispersing Agent-Selection Methodology......................................... ...........21









Charge Controlling Agents-Selection Methodology...............................................24

6 RAW MATERIALS CHARACTERIZATION AND EXPERIMENTAL
TECH N IQU ES ...................... .. ...................... .. ........ .......... 25

Scanning Electron M icroscopy (SEM )........................................... .....................25
Energy Dispersive x-ray Spectrometry (EDS) ................................. ............... 27
Nuclear Magnetic Resonance Spectroscopy (NMR)...............................................28
P lan etary B all M ill ........................................................................ .. ................ .. 2 9
M isonix Sonicator 3000 .................. ............................ .... .. .. .. ........ .... 30
Suspension Preparation........ ............................................................ .......... .....30
Rheometer .................................................. 30
V iscosity M easurem ents ........... ......... ..................................... ........................ 31
Optical Density Measurement Equipment Setup..................................................31

7 EFFECT OF POLYMER ADSORPTION ON RHEOLOGY AND SOLIDS
LOADING OF THE SU SPEN SION .................................. ..................................... 33

Determination of the Optimum Amount of Polymer............................................... 33
Optimum Am ount of Polystyrene ............................................... ............... 33
O ptim um A m ount of L P ........................................................................ .. .... 33
Optimum Amount of Polybutadiene ........... ....................... .................34
Comparison of the Optimum Amounts of Dispersants ...............................36
Determination of the Optimum Amount of Charge Controlling Agent .....................36
Optimum Amount of CCA7 in the LP1 suspension .......................... .........37
Optimum amount of CCA7 in the Polystyrene Suspension.............................37
Comparison of the Optimum Amounts of CCA ........................... ...............38

8 EFFECT OF RELATIVE VISCOSITY ON SOLIDS LOADING OF THE NON
POLAR SILICON CARBIDE SUSPENSION...................................... ..................40

Relative Viscosity on Solids Loading for the Polybutadiene Stabilized
S u sp en sio n ........................ ..... .............. .... ........................... .. ............... 4 1
Relative Viscosity on Solids Loading Dependence for the LP1 Stabilized
Suspension ............. ...... ....................... ....... .......... ....... ................... 42
Solids Loading Dependence on Relative Viscosity for the Polystyrene Stabilized
Su sp en sion ............................................................. ................ 4 3
Comparison of the Stabilization Methods ..............................................................44

9 EFFECT OF OPTICAL DENSITY VARIANCE WITH VOLTAGE....................46

Optical Density Variance with Voltage for LP1 ............ ................. .....................46
Optical Density Variance with Voltage for Polystyrene .........................................49
Comparison of Optical Density Variance with Voltage for LP 1 and Polystyrene.....51

10 EFFECT OF OPTICAL DENSITY VARIANCE WITH TIME ..............................54









Optical Density Variance with Time for LP .............. .....................................54
Optical Density Variance with Time for Polystyrene.......................... .............56
Comparison of Optical Density Variance with Time for LP1 and Polystyrene .........58

11 ANALYSIS OF THE ELECTROPHORETIC DEPOSITION..............................60

Scanning Electron M microscope Images ............................ ..... ....................... 61
P oly sty ren e S am ples........... ...... .............................. ................ .. .... .... .. ..6 1
LP 1 Sam ples .................................................................... ......... 63
D digital C am era Pictures ...........................................................................64

12 C O N C L U SIO N ......... ......................................................................... ........ .. ..... .. 69

LIST OF REFEREN CES ............................................................................. 71

BIO GRAPH ICAL SK ETCH .................................................. ............................... 74
















LIST OF FIGURES


Figure page

2-1 Block diagram of the principle of the solid freeform fabrication (SFF) technique....4

2-2 The stereo lithographic m machine ........................................... ......................... 5

2-3 The electro-photographic solid freeform fabrication (ESFF) machine....................6

2-4 A schematic of the electro-photographic solid freeform fabrication (ESFF)
m ach in e .............................................................................. 7

2-5 A sketch showing the principle of the electro-photographic solid freeform
fabrication (E SFF ) m machine ............................................................ .....................7

3-1 The double layer consisting of the three regions................... ................................... 11

3-2 The variation of potential energy between two particles in a liquid medium due to
van der Waals attraction and electric double layer repulsion..............................13

4-1 The variation of shear stress and viscosity with shear rate. ....................................16

5-1 The chemical structures for trans and cis decahydronapthalene. ..........................21

5-2 Separation distance (nm) for SiC particles with the van der Waals interaction
energy (kT) in the sphere-sphere interaction mode...............................................23

6-1 SEM picture of the 6H-alpha- silicon carbide (UF Grade 15).............................26

6-2 SEM picture of the charge controlling agent (CCA7)............... ................27

6-3 EDS of the charge controlling agent 7 (CCA7) .....................................................27

6-4 The carbon (13C) NMR for the LP1 polymer ............................... .................28

6-5 The proton (1H) NMR for the LP1 polymer..........................................................29

6-6 Flowchart for the suspension preparation ..................................... .................32

7-1 Optimum amount of polystyrene required for complete coverage of the SiC
su rfa c e .. ................................................................................... 3 4









7-2 Optimum amount of LP1 required for complete coverage of the SiC surface.........35

7-3 Optimum amount of polybutadiene required for complete coverage of the SiC
su rface ............................................................................ 3 5

7-4 5 vol% SiC in decahydronapthalene with varying amounts of the dispersants
polystyrene(PS), polybutadiene(PB) and LP1 used.......................... ..................36

7-5 The amount of LP1 added is 0.4 wt% SiC for the 5 vol% SiC in
decahydronapthalene. The deposition was done for 60 seconds and the DC
voltage applied w as +4kV ............................................... ............................. 38

7-6 The amount of polystyrene added is 0.4 wt% SiC for the 5 vol% SiC in
decahydronapthalene. The deposition was done for 60 seconds and the DC
voltage applied w as +4kV ............................................... ............................. 39

7-7 The amount of LP1 and polystyrene(PS) added are 0.4 wt% SiC for the 5 vol%
SiC in decahydronapthalene. The deposition time was 60 seconds and the DC
voltage applied w as +4kV ............................................ ..... ........................ 39

8-1 The variation of shear stress with shear rate for a 0.4 wt% LP1 stabilized slurry
with 5 vol% SiC in decahydronapthalene. .................................... .................40

8-2 The variation of shear stress with viscosity for a 0.4 wt% LP1 stabilized slurry
with 5 vol% SiC in decahydronapthalene. .................................... .................41

8-3 Variation of relative viscosity with solids loading of SiC in decahydronapthalene
with 0.3 wt% SiC, being the polybutadiene (PB) amount. .....................................42

8-4 Variation of relative viscosity with solids loading of SiC in decahydronapthalene
with 0.4 wt%/ SiC, being the LP1 amount. ........................................ ............... 43

8-5 Variation of relative viscosity with solids loading of SiC in decahydronapthalene
with 0.4 wt% SiC, being the polystyrene (PS) amount........................................44

8-6 Variation of relative viscosity with solids loading of SiC in decahydronapthalene
with 0.4 wt%/ SiC, being the LP1 and polystyrene (PS) amounts and 0.3 wt% SiC
the polybutadiene (PB) am ount ........................................ ........................... 45

9-1 Variation of optical density with voltage for a LP 1 slurry without charge
controlling agents and with a deposition time of 120 seconds.............................47

9-2 Variation of optical density with voltage for a LP 1 slurry with charge controlling
agent 7 and a deposition time of 60 seconds ................... ............................ 48

9-3 Variation of optical density with voltage for a LP 1 slurry with charge controlling
agents and with a deposition time of 120 seconds. ...............................................49









9-4 Variation of optical density with voltage for polystyrene slurry without charge
controlling agents and a deposition time of 60 seconds ........................................50

9-5 Variation of optical density with voltage for polystyrene slurry with charge
controlling agent 7 and a deposition time of 60 seconds. ........................................51

9-6 Variation of optical density with voltage for polystyrene slurry with charge
controlling agent 7 and a deposition time of 120 seconds. .....................................52

9-7 Variance of optical density with voltage for 5 vol% SiC in decalin with 0.4 wt%
SiC being the LP1 and polystyrene (PS) amounts. .............................................53

10-1 Variation of optical density with time for a LP1 slurry without charge controlling
agents and a deposition voltage of +2kV. .............................................................55

10-2 Variation of optical density with time for a LP1 slurry without charge controlling
agents and a deposition voltage of +4kV. ........................................... ..... ..........55

10-3 Variation of optical density with time for a LP1 slurry with charge controlling
agent 7 and a deposition voltage of +2kV ............... ....... .. ............... ......... 56

10-4 Variation of optical density with time for a polystyrene slurry without charge
controlling agents and a deposition voltage of +4kV ......... ...... ... .............. 57

10-5 Variation of optical density with time for a polystyrene slurry with charge
controlling agent 7 and a deposition voltage of +2kV. .............. ........ ..........57

10-6 Variation of optical density with time for a polystyrene slurry with charge
controlling agent 7 and a deposition voltage of +4kV. .............. ........ ..........58

10-7 The variation of optical density with time for a 5 vol% SiC in
decahydronapthalene with 0.4 wt% SiC being the LP1 and polystyrene (PS)
am ou n ts. .......................................................... ................ 5 9

11-1 SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension in
decahydronapthalene with polystyrene. ...................................... ............... 62

11-2 SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension in
decahydronapthalene with polystyrene and the charge controlling agent 7.............62

11-3 SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension in
decahydronapthalene with LP1 polymer ....................................... ............... 63

11-4 SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension in
decahydronapthalene with LP1 polymer and the charge controlling agent 7.........64









11-5 Digital camera picture of the steel electrode after it was dipped into the 5 vol%
SiC in decahydronapthalene with LP1 polymer suspension and kept for 60
seconds without the application of a voltage. .................................. .................65

11-6 Digital camera picture of the steel electrode after it was dipped into the 5 vol%
SiC in decahydronapthalene suspension with LP1 polymer and kept for 60
seconds with the application of a voltage of +4kV .............. ......... ............... 66

11-7 Digital camera picture of the steel electrode after it was dipped into the 5 vol%
SiC in decahydronapthalene suspension with the polystyrene polymer and kept
for 60 seconds without the application of a voltage..............................................66

11-8 Digital camera picture of the steel electrode after it was dipped into the 5 vol%
SiC in decahydronapthalene suspension with LP1 polymer and kept for 60
seconds with the application of +4kV and for another 60 seconds with the
application of -4kV ................................... ............ ...... ...... .. ...... ...... 68















Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

DEVELOPMENT OF AN ALPHA SILICON CARBIDE BASED LIQUID TONER
FOR ELECTRO-PHOTOGRAPHIC SOLID FREEFORM FABRICATION

By

NAVIN JOSE MANJOORAN

May 2003

Chair: Wolfgang. M. Sigmund
Major Department: Materials Science and Engineering

Most industrial ceramic processing applications require slurries that can be easily

poured with the highest solids loading. This helps in making the final cast have a good

packing uniformity and reduces the sintering shrinkage. Rheological studies are carried

out with alpha silicon carbide slurries in a non-polar media using polystyrene,

polybutadiene and LP1 dispersants. The experimental data were fit into the Krieger-

Dougherty equation to find out the maximum solids loading and colloidal properties of

the slurry.

A novel solid freeform method, "Electro-photographic Solid Freeform Fabrication"

(ESFF), needs specific qualities for solid (powder) and liquid (slurry) toner (electronic

ink). The development of a liquid toner, study of its flow behavior and electrophoretic

tests confirming that the toner could be used for ESFF are carried out and the data

analyzed.














CHAPTER 1
INTRODUCTION

A novel Solid Freeform Fabrication (SFF) method, referred to as Electro-

photographic Solid Freeform Fabrication (ESFF), needs specific qualities for a toner

material (solid or liquid). By using a liquid toner we can deal with sub-micron size

powders, which would help in improving the resolution of the prototype obtained. Here,

we deal with preparing a liquid toner and carrying out tests to show that the liquid toner

can be used for the solid freeform fabrication process. A liquid toner consists of sub-

micron sized particles dispersed in a non-polar solvent, with polymers acting as

dispersants and charge controlling agents maintaining the charge. Rheology studies were

done to find the maximum solids loading that can be obtained for the slurries with

polystyrene, LP1 and polybutadiene. The models were fit to the Krieger-Dougherty

equation. Electrophoretic tests were done to study the variance of optical density with

voltage and time.

Chapter 2 deals with an introduction to solid freeform fabrication. A brief history,

how the process works, the advantages and the applications of SFF are described here.

The later part of the chapter deals with a novel SFF technique referred to as electro-

photographic solid freeform fabrication. In chapter 3, a discussion is based on basic

theories and concepts that exist in colloidal processing, mainly, the various stabilization

methods and coagulation. The dependence of viscosity on packing fraction, the Krieger-

Dougherty equation and basic concepts on rheology are discussed in chapter 4.Chapter 5

deals with the methodology for the materials selection. How and why the specific









materials were chosen for the experiments are explained. In chapter 6, the various

characterizations on the raw materials taken are explained. The methodology for the

experiments and the equipment used for the various experiments are also mentioned

here. Chapter 7 deals with determining the amount of polymer needed to completely

cover the silicon carbide particle and to determine the amount of charge controlling agent

needed to get the required electrophoretic deposition. The dependence of relative

viscosity on solids loading of the slurry, the Krieger- Dougherty fit curves and the

determination of the maximum solids loading for the slurry are concentrated in chapter 8.

Chapter 9 deals with the study of the variance of optical density with voltage and to find

out the best voltage region to carry out the electrophoretic depositions at. In chapter 10,

the concentration is on the study of the variance of optical density with time for the

slurries having polystyrene as the polymer and those having LP1 as the polymer. The

analysis of the electrophoretic deposition is seen in Chapter 11. The pictures of the

deposition are also present here. Chapter 12 gives a brief conclusion to the results of the

experiments.














CHAPTER 2
GENERAL THEORIES AND CONCEPTS IN SOLID FREEFORM FABRICATION

History

The thought of making three-dimensional objects, without the use of any tooling

methods have interested scientists for many years [1]. Technique's using a specific

hardening feature by the laser beam, were available in the early eighties [2]. Hull and

Charles [3] patented the stereolithography apparatus in 1986. By this process three-

dimensional plastic parts could be created directly from Computer Aided Design (CAD)

data. From then on many Solid Freeform Fabrication (SFF) techniques have been

developed.

What Is SFF?

Solid Freeform Fabrication (SFF) is a method to fabricate custom three-

dimensional objects with desired properties from computer data [4, 5]. This is basically a

layer-by-layer manufacturing method of three-dimensional objects. Due to this layer-by-

layer building approach, quicker and cheaper production of prototypes could be made.

First, the solid model of the part to be manufactured is created in CAD software. This is

then exported to the SFF process via a software interface [4]. The software interface is

java orjava2 and the program used is the solid slicer. The SFF process deposits various

materials layer by layer in the shape of the cross-section of the solid to create the part. A

simplified flow diagram is shown in figure 2-1.


































Figure 2-1.Block diagram of the principle of the solid freeform fabrication (SFF)
technique

The automation for the entire process is also possible. In theory, since the

prototypes can be produced very fast the solid freeform fabrication is also referred to as

Rapid Prototyping (RP).

Solid freeform fabrication methods can be classified on the basis of the raw

material used, lighting of photopolymers, and by the application range for which it is

used [2]. The earliest form of SFF was stereolithography [3, 5]. Stereolithography uses an

Ultra Violet (UV) laser (generally a helium-cadmium laser) to create successive cross

sections of three-dimensional objects within a vat of liquid photopolymer. This technique

makes use of photo reactive polymers, those that react with UV light. When UV light

strikes the photo reactive polymer resin, it gets solidified. Thus, in this manner a layer of

the three-dimensional model could be formed. The process is continued by either









lowering the object into the vat of the polymer or by spreading a new layer on the object

in order to make the next and subsequent layers form the solid part. A schematic diagram

of the stereolithography prototyping system stated by Hull and Charles [2] is shown in

figure 2-2. The parts that are built using stereolithography are durable, but fragile. The

stereo lithographic machine is accurate with building parts containing intricate details and

complex shapes. 3D systems of Valencia, CA, since 1988 is the industry leader in selling

RP machines particularly those using stereo lithographic techniques.



Com puter
Control

U V Light

Resin 3D P arts Z









Figure 2-2.The stereo lithographic machine [2]

SFF has been associated with manufacturing environments, where it is used for the

rapid production of visual models, low run tooling and functional objects [6]. The

additive nature of SFF techniques, offers great promise for producing objects with unique

material combinations and geometries, which could not be attained by traditional

methods and are different from most machining processes (milling, drilling, grinding,

etc), as these are subtractive processes that remove material from a solid block. So, it can

be used in diverse fields as aerospace, electronics, architecture, biomedical engineering

and archeology [6]. SFF allows designers to quickly create tangible prototypes of their









designs rather than two-dimensional pictures. These help in making less expensive and

excellent visual aids for communicating ideas with co-workers or customers. It can also

be used for design testing. For small production runs and complicated objects, SFF is the

best process available. The time required to build the prototype depends on the size and

complexity of the object. The time saving allows manufacturers to bring products to the

market faster and more economically [6].

Electro-photographic Solid Freeform Fabrication (ESFF) is a novel solid freeform

fabrication technique. It uses the electro-photography technique to deposit particles layer-

by-layer on a specially designed platform. [1, 7, 8] (Figure 2-3)


PConrnngSl-;rntw system
Pnnling, slpml .1
Build Platfo3rm '

II













Figure 2-3.The electro-photographic solid freeform fabrication (ESFF) machine [8]

During the electro-photography process, the particles are picked up by a charged

surface and deposited on an oppositely charged surface. Therefore, it is important to

know the characteristics, especially the charging characteristics of the particles in this

process. Kumar [1] has designed a test-bed, ESFF machine (Figure 2-4), which deposits










the particles in the required regions, layer-by-layer, on a numerically controlled two-axis

platform.




Eiec- r-pholog r ;ip1h engine Build platform
Compaction platform -, Radiant Heater



Structural frame

Z-axis lead screw
Driven linear actuator
X-axis belt driven
Linear actuator






Figure 2-4.A schematic of the electro-photographic solid freeform fabrication (ESFF)
machine [8]

A heating and compacting system is used to fuse each layer of particles deposited.

Figure 2-5, shows a schematic representation of how the ESFF process works. The

photoconductor drum is charged with the help of a charging roller using direct contact

charging. The laser image projector makes the image on the photoconductor drum by

removing the charge from the drum at the required regions. From the image developer


Laser Image projector
Charging Roller I Image developer

Photoconductor
drum

Radiant or contJ-
heater Build platform




Moving platform


Figure 2-5.A sketch showing the principle of the electro-photographic solid freeform
fabrication (ESFF) machine [8]










the particles are attracted to the magnetic development drum, by applying a high voltage

on the drum. The particles then get transferred to the photoconductor drum at the regions

required because of their opposite polarity. The developed image is then transferred onto

the build platform with the help of an electric field and then permanently fixed by fusing.

The photoconductor surface needs to be cleaned using physical or electrical methods,

before the process is repeated to get the three-dimensional object.

Of late, there has been a great demand worldwide for electro-photography based

full color printing devices for both Small Office and Home Office (SOHO) and for the

heavy volume commercial application [9, 10, 11, and 12]. The printing "toner"

(electronic ink) can be either in the powder form (solid toner) or the sub-micron sized

toner particles can be suspended in a dielectric liquid (liquid toner). There has been an

increasing demand for a high quality short run printing and the liquid development

process using a liquid toner can meet this demand well because with this we can achieve

high resolution, good image quality and a better packing uniformity [13]. Thus, liquid

toners are important and there is the need to develop a liquid toner for the ESFF process.














CHAPTER 3
BASIC THEORIES AND CONCEPTS IN COLLOIDAL PROCESSING

A colloid consists of two phases [14]. One of the phases, referred to as the

dispersion medium is generally a solid, liquid or a gas and the other, the finely dispersed

particulate phase, is either a gas, liquid or a solid. It is seen that compared to powder

consolidation methods, using colloidal suspensions, leads to a much better packing

uniformity in the green body for sub-micron sized particles. This helps in achieving

superior micro-structural properties during sintering. The use of a high solids loading

slurry, reduces the shrinkage due to sintering, during the compaction process. Moreover,

the sinterability is also better using a high solids loading slurry. However, the difficulty

lies in making a colloidal suspension with the highest possible solids loading and a low

enough viscosity so that it can be poured. [14]

For colloidal suspensions, to give the best packing uniformity, the suspension

prepared must be stable. When particles are close together, the attractive van der Waals

forces tend to coagulate the particles. To avoid coagulation, various stabilization methods

can be used which are explained below. A stable high solids loading colloidal suspension

can be consolidated to a densely packed structure.

Stabilization Methods for Colloids

For particles in a liquid dispersing medium, attractive van der Waals forces tend to

flocculate the particles. To avoid flocculation or coagulation of particles, a reduction in

the attractive forces is needed and the techniques used to achieve this are based on

introduction of repulsive forces [14]. The repulsion between particles, based on the









electrostatic charges on the particles is termed as electrostatic stabilization. The

stabilization mechanism is termed as polymeric stabilization, when the repulsion is

produced by polymer molecules, adsorbed or chemically attached, onto the particle

surfaces or existing freely in the solution. When repulsion is a consequence of the

combination of electrostatic and polymeric stabilization mechanisms it is termed as

electrosteric stabilization [14].

Electrostatic Stabilization

In electrostatic stabilization, the repulsion is not between the charged particles. A

diffuse electrical double layer of charge is produced between the particles and this

interaction formed between the diffused double layers formed is the cause for the

repulsion. For a particle covered by a diffuse double layer, the shear slippage occurs at a

distance from the surface and the potential at this shear slippage is termed as the zeta

potential. The zeta potential is the potential at the surface of the electrokinetic unit,

moving through the liquid medium, as determined from the measured electrophoretic

mobility [14,15].

For ceramic particles dispersed in a solution the main process by which they can

acquire a surface charge is by the adsorption of ions from the solution. The surfaces of

oxide particles are normally hydrated in water. The adsorption of H ions produces a

positive charge on the oxide surface and similarly the adsorption of the OH- ions

produces a negative charge on the oxide surface. At some intermediate pH, the adsorption

ofH+ ions will balance that of the OH- ions. This intermediate pH is called as the Point of

Zero Charge (PZC)[14]. At this point, the particle surface is effectively neutral.

It is observed that the measurement of the surface potential is difficult, as some

finite ionic dimensions, could approach only up to a certain distance of the interface. This








led to the stern layer effect. The stern layer effect states that the double layer consists of

three regions. The outermost layer is called the 'diffuse double layer.' The layer formed

due to the adsorption and which lies adjacent to the particles interface is called the 'inner

Helmholtz layer.'





Stern plane

e ....... ...-...... Shear plane
e.... e e
Diffus e d-/
I / ..."'""" / \Diffuse double layer
e Z -.., .4


\e e
',\
$",


to


Distance

Figure 3-1.The double layer consisting of the three regions [15]

The layer where the counter ions were arranged at a distance form the interface is called

as the 'outer Helmholtz layer'. It is easier to measure the potential at a small distance

form the particle surface, that is, at the surface of the stern layer and this potential is









referred to as the zeta potential. The pH where the charge on the stem layer is zero,

rather the zeta potential is zero, is referred to as the Iso-Electric Point (IEP).

Double Layer Repulsion

It is seen that for colloidal particles, when two particles come closer together their

double layers start to overlap. If the particles carry the same charge, repulsion is seen

after their double layers overlap resulting from inter-penetration of the two diffuse layers.

This repulsion prevents further movement of the particles closer together and is believed

to be the reason for the stability of the suspension. The universally accepted theory for

the interaction between electrical double layers is the DLVO theory (after Derjaguin,

Landau, Verwey and Overbeek) [14, 16].

DLVO Theory

Named after Derjaguin, Landau, Verwey and Overbeek, this theory explains the

interactive forces acting between the electric double layers. The theory states that the

total interaction energy is the sum of the attractive potential energy and the repulsive

potential energy.

VT = VA + VR [3.1]

The electric double layer stabilization is seen when the double layers of similarly

charged particles approach each other and the repulsive forces between them are large

enough to overcome the van der Waals forces of attraction.

Polymeric Stabilization

This is the stabilization of the colloidal particles by organic polymer molecules. It

can be accomplished by either steric stabilization or depletion stabilization. When the

stabilization mechanism is achieved by polymer molecules adsorbed or attached to the

colloidal particle, the mechanism is referred to as steric stabilization. When the










stabilization is achieved by polymer molecules in the free solution it is termed as

depletion stabilization [14].











'.,VR Electric Double Layer Repulsion



S.max.





0
Distance W s

Z *"" V .
0
'" ," van der Waals attraction


Figure 3-2.The variation of potential energy between two particles in a liquid medium
due to van der Waals attraction and electric double layer repulsion [15,16]

Electrosteric Stabilization

Electrosteric stabilization requires the presence of both the adsorbed polymers and

the double layer repulsion a combination of the electrostatic and steric forces. This can

be achieved by using a charged particle and a neutral polymer, by using a neutral particle

and a charged polymer or by using a charged particle and a charged polymer [14].






14


Coagulation

The potential barrier decides the stability of a suspension. In most colloids the

particles remain suspended only when the energy barrier is greater than kT. In other

cases, it is seen that the particles tend to adhere to each other. If this process is reversible

it is termed as flocculation and if it is irreversible it is termed as coagulation. A coagulate

is defined as a set of particles in suspension held together by attractive van der Waals

forces [14, 15].














CHAPTER 4
BASIC CONCEPTS AND THEORIES IN UNDERSTANDING THE RHEOLOGICAL
PROPERTIES FOR PARTICULATE SUSPENSIONS

Rheology is the study of deformation and flow of matter. As the stability of the

dispersion is dependent on the final structural outcome of the consolidated solid, it is

important to understand and know the theological properties of the colloidal suspension.

A good colloidal suspension is one that has a high solids loading and a low viscosity. The

high solids loading helps obtain a high packing density during the compaction process.

The viscosity of the suspension should be low enough so that it can be poured easily [16,

17, 18].

Importance of Rheological properties

The most important property used to describe the flow of a liquid is its viscosity.

By carefully analyzing the viscosity we can find out the maximum solids loading that can

be achieved for the suspension. This helps in making suspensions with high packing

densities during compaction and reduces the shrinkage.

The viscosity is defined as

1= T\y [4.1]

where, rI is the viscosity, T is the shear stress and y is the shear rate.

From the variation of viscosity with shear rate of the suspension we can know if the

liquid shows a Newtonian behavior or not. For Newtonian liquids, the viscosity is

independent of the shear rate of the suspension. However, for most of the suspensions

generally used, such as polymer suspensions or colloidal suspensions the viscosity







16


changes with shear rate of the suspension and are therefore termed as non-Newtonian

liquids. Therefore in these cases the viscosity will be a function of shear rate.

Depending on how the viscosity varies with shear rate we can have different kinds

of liquids. If the viscosity of the suspension decreases with shear rate it is called as shear

thinning or pseudoplastic liquid and if the viscosity increases with the shear rate it is

called as shear thickening or dilatancy. We have the thixotropic behavior when the

viscosity depends not only on the shear rate but also on time.





sm-rAWWW

iP&oRATE LSEAnR IATM
A




mSTERAB VicABSrENTv

SEAR RAFTE ~ SHIEAR RATE





v-i- v

SMEAR RATE ESHA F ATE
C'


Figure 4-1.The variation of shear stress and viscosity with shear rate. A. newtonian
Liquid, B. dilatant liquid and C. pseudoplastic liquid

Solids Loading

We consider the particles to be hard spheres, for better understanding of the effect

of the concentration of the particles. This means we discard the presence of charged









electrical double layers or adsorbed polymers. According to Einstein, the increase in the

viscosity is caused by the increase in the solids loading as shown in the equation below

l= no ( 1 + 2.5b ) [4.3]

where, rI is the viscosity of the suspension, rlo is the viscosity of the liquid medium, 4 is

the volume fraction of the particles.

A more generalized equation is

rl= no ( 1 + ki ) [4.4]

where, kl is the Einstein's coefficient, which is 2.5 for hard spheres.

However this equation particularly deals with dilute suspensions (when there is no

interaction between the particles). For concentrated suspensions, the equation becomes

more complex and is given by,

f= no ( 1 + klk + k242 + k343 + k444+ ...) [4.5]

Generally the viscosity is expressed as the relative viscosity (rir) and is the ratio of

the viscosity of the suspension (r ) to the viscosity of the liquid medium (lo).

As more and more particles are added into the solution, there is an increase in the

solids loading and finally at a certain solids loading the viscosity reaches infinity. This

limiting value is called the maximum solids loading (4m). At the maximum volume

fraction, the particles in the slurry are so close together that their average separation

distance is almost zero and this makes their flow impossible [18,19]. The maximum

solids loading is around 0.65 for hard spheres and maybe around 0.4 0.5 for colloidal

suspensions in which the interaction between the particles are significant. Depending on

the slurry that is prepared we can have variations in the maximum solids loading.









For mono-size spheres, the Krieger and Dougherty equation explained [14, 16]

below can be used to calculate the maximum solids loading which is given by


S= 1-7 [4.6]

where [fr] is the intrinsic viscosity and 4m is the maximum solids loading.

Particle Size Analysis

The particle size and size distribution does have an impact on the viscosity of the

colloidal suspension. It is seen that the Krieger Dougherty fit works only when the

particles are mono dispersed. When the particles are poly-dispersed it is seen that the

maximum solids loading is different compared to the mono-dispersed particles as the

smaller particles can occupy the voids between the larger particles. For mono sized

particles the viscosity reaches a maximum value at a lower solids loading. Thixotrophic

behavior or lowering of the maximum solids loading is seen when the majority of the

particles are of the smaller size range. This happens as the particles have a large specific

surface area for the solvent and dispersant to bind to. Dilatancy, due to the obstruction of

flow of particles leads to a lowering of the solids loading in the suspensions having a

majority of particles of the larger size.

Polymer Adsorbed Layers

The adsorption (chemical bonding) of polymer layers onto the surface of particles

can result in a better stabilization of the colloidal suspension. If the polymers are organic

in nature, steric stabilization is seen. If the polymers are ionizable, the stabilization

mechanism is a combination of the steric and the electrostatic methods- electrosteric

stabilization. The adsorbed layer of the polymer should be such that they can overcome

the van der Waals forces of attraction and thereby prevent the adherence of the particles.






19


The polymer additions of the amount of 0.4-0.5 % of the weight of the particles can help

achieve fairly low viscosities at high solids loading [14].














CHAPTER 5
METHODOLOGY FOR LIQUID TONER MATERIAL SELECTION

In liquid development systems, non-aqueous dispersions consisting of sub-micron

sized particles stabilized in an adsorbed layer of polymer and charge control agents in

aliphatic hydrocarbons are used as toners [20].

Solvent-Selection Methodology

As, ISOPAR (ISO- PARaffinic hydrocarbon highly branched alkanes with 7-15

carbon atoms), the solvent used in most industrial applications for the development for

the liquid toner, is not well defined, a solvent with similar properties as of ISOPAR and a

clearly defined structure was selected. Thus, decahydronapthalene (C1oH18) was used as

the solvent [18, 21, and 22]. The properties considered were a high flash point (135F for

decahydronapthalene), non-polar nature, non- conductivity, chemical inertness, relatively

non-viscous nature and volatility. Decahydronapthalene meets the majority of these

requirements. The chemical structure for decahydronapthalene is given in figure 5-1.

Ceramic Particles-Selection Methodology

Silicon Carbide (SiC), sub-micron sized particles were used, as they are an

important ceramic for structural and electrical applications, because of their excellent

mechanical and electrical properties at high temperatures [18, 19]. Sub-micron sized

particles were made use of to produce very high-resolution images [13]. Silicon carbide

has been used as an industrial product for more than hundred years. It can be used for a

broad range of applications like high temperature semiconductors, medical, biomaterials

and light weight- high strength structural materials.












H



H
H


trans- Decalin


H



H


H
cis Decalin


Figure 5-1.The chemical structures for trans and cis decahydronapthalene.

Dispersing Agent-Selection Methodology

The adsorbed layer of the polymer should be such that they can overcome the van

der Waals forces of attraction and thereby prevent the adherence between the particles.

To find suitable dispersing agents for the SiC and C10H18 system, the refractive indices

and dielectric constants for silicon carbide and decahydronapthalene were substituted in









the Tabor-Winterton equation mentioned below and the Hamaker constant was calculated

[17].

3kT r i (0) -- 8(0) 3ho 3n n
A131 4 ,(0)+E3(0)J 16/2 (vI 2 [5.1]

A ,3 = Hamaker constant
k Boltzmann's constant
T Temperature
ei(0) = 0 frequency dielectric constant
h = Plank's constant
CO, = plasma frequency, UV cutoff
(usually around 3x 101 Hz)
n = index of refraction in the visible range

For the SiC and C1oH18 system the refractive indices are 2.649 [23] and 1.475 [24]

respectively and the dielectric constants are 9.71 [25] and 2.196 [26] respectively at

298K. Using these values in the Tabor Winterton Approximation (TWA), the Hamaker

constant was calculated to be 2.233*10-19J for the SiC-C1oH1i system [16]. A graph, for

sphere-sphere interactions, at 298K, with the Hamaker constant of the system, showing

the variation of separation distance of SiC particles with respect to the van der Waals

interaction energy was plot [figure 5-2].

The figure 5-2 shows an increase in the magnitude of the van der Waals interaction

energy as the particle separation distance decreases. The increase in the van der Waals

interaction energy can be seen to start when the separation distance is 40 nm. So, if we

can keep the particles 40 nm apart, by using a polymer, we could avoid the coagulation of

the particles due to van der Waals interaction. Using the solubility parameter handbook,

the solubility parameters for polymers [polybutadiene (18.0 (MPa)0 5) and polystyrene

(18.6 (MPa)0.5) ] having similar solubility parameter values with that of C1oH1i (18.0

(MPa)o5 ) were chosen [27]. Now, using the formula for the radius of gyration(r) given










below the approximate molecular weights required for these polymers were calculated

[14].



SPHERE/SPHERE INTERACTIONS


0


-2

r_
3 -4



LU

I -8
u,
S-10


M -12


-14


-amm -mmm mmmm----
00 10.0 203.0 300.0 40.0 500.0 60






I INTERACTIONS____________
*

o*

*


Separation Distance (nm) vU UU", UI UULtIL
Hamaker constant:2.23*10-19 J

Figure 5-2.Separation distance (nm) for SiC particles with the van der Waals interaction
energy (kT) in the sphere-sphere interaction mode. The Hamaker constant for
the calculation was taken to be 2.23*10-19J and the temperature was 298K

r2 cn2 [5.2]

where, '1' is the segment length, 'c' is a constant factor and 'n' is the number of

segments.

The average molecular weights required for polystyrene and polybutadiene were

calculated to be in the order of 105 and 103, respectively. Actual solubility tests showed

that polybutadiene and polystyrene were soluble in the non-polar solvent. Thus,

polybutadiene, polystyrene and for comparison, Hypermer LP1 (High performance

polymer- an industrially used polymer) were chosen.


Temperature : 293 K
Particle radius:0.55 [im
J- W l t ts ti


!


).0







*SPHERE/SPHERE
INTERACTIONS


-*/






24


Charge Controlling Agents-Selection Methodology

In industrial systems, particle charge controlling agents are added to control the

magnitude and sign of the surface charge of the particles [18, 28, 29, and 30]. Therefore,

CCA7, an industrially used negative charging agent, was used to provide the charge.














CHAPTER 6
RAW MATERIALS CHARACTERIZATION AND EXPERIMENTAL TECHNIQUES


6H-alpha silicon carbide (Grade UF-15, H.C.Starck, Canada), cis-trans

decahydronapthalene (Aldrich), polystyrene (Aldrich), polybutadiene (Aldrich), LP1

(Uniqema, Belgium) and charge controlling agent 7 (Avecia-Inc) were the starting

materials. The average molecular weights for polystyrene, polybutadiene and LP1 are

-230000, 5000 and 6000 respectively. The Silicon Carbide (SiC) and Charge

Controlling Agent 7 (CCA7), particle sizes, were measured with the Brookhaven

instruments Zeta plus particle sizing and were found to yield a dso of 0.520.02 [m and

0.420.02 rm respectively. The surface area of SiC, measured by BET (AREAMETER

II) N2 adsorption is 15m2/g (H.C. Starck). Polystyrene, polybutadiene and LP1 are used

as dispersants for the different experiments and their amounts are based on the weight

percent of the dry SiC powder.

Table 6-1.Raw materials used for the experiments
S.No Material Company D50, Mw, BET surface area
1 6H-alpha- silicon carbide H.C.Starck, Canada D50 of 0.520.02 rm, 15m2/g
2 Cis-trans decahydronapthalene Aldrich 99+% purity
3 Polystyrene Aldrich Mw 230,000
4 Polybutadiene Aldrich Mw 5,000
5 LP1 Uniqema, Belgium Mw 6,000
6 Charge controlling agent 7 Avecia-Inc D50 of 0.420.02 [im


Scanning Electron Microscopy (SEM)

The SEM imaging was carried out using the JEOL JSM6330F. The JEOL 6330 is a

cold field emission scanning electron microscope. The cold field emission has the









advantage of high brightness (large current density) and small beam diameter (high

resolution) at low accelerating voltages to allow imaging of soft polymeric materials

without causing damage to the sample. Resolution of the instrument is around 1.5nm

depending on the sample. The instrument has an energy dispersive X-ray spectrometer

(EDS) for elemental analysis.


Figure 6-1.SEM picture of the 6H-alpha- silicon carbide (UF Grade 15)

The SEM image for SiC was taken at 10,000X magnification with a working

distance of 14.6mm. The figure 6-1 shows that the particles are mainly spherical and are

more or less of the same size and shape.

The SEM picture for the CCA7 was taken at 8,000X magnification with a working

distance of 16.2mm. The figure 6-2 shows that the particles are mainly rod shaped.



































Figure 6-2.SEM picture of the charge controlling agent (CCA7)

Energy Dispersive x-ray Spectrometry (EDS)

The EDS was carried out using the JEOL JSM6330F SEM. The instrument has an

energy dispersive X-ray spectrometer (EDS) for elemental analysis which was used. The

EDS of CCA7 shows that the negative charge controlling agent is mainly a chromium

complex (figure 6-3).

Full scale = 491 cps Cursor: 8.9675 keV


I 6 0 12 14 16 18 20
I e"*


Figure 6-3.EDS of the charge controlling agent 7 (CCA7)


C


CF


Cl

CF

IL C Cu


UI












Nuclear Magnetic Resonance Spectroscopy (NMR)


Nuclear magnetic resonance spectroscopy makes use of the spin of the media to


study physical, chemical, and biological properties of matter. Nuclear magnetic


resonance is a phenomenon which occurs when the nuclei of certain atoms are immersed


in a static magnetic field and exposed to a second oscillating magnetic field. Dependent


upon whether they possess the property called spin, some nuclei experience this


phenomenon, and others do not. The carbon (13C) NMR and the proton (1H) NMR for the


LP1 polymer were taken. The NMR for the LP1 polymer shows that the polymer consists


of single bonded carbon and hydrogen


""
,,,
h,~D
om~,
m-m~~i,
h~ N


0 ppm


Figure 6-4.The carbon (13C) NMR for the LP1 polymer


50 140 120 100 80 60 40















































3 2 1 0 ppm

0.51 6.33
0.59 1.00 0.99

Figure 6-5.The proton (1H) NMR for the LP1 polymer

Planetary Ball Mill

The pulverisette 5" laboratory planetary ball mill with a maximum speed of

350rpm was used initially for the lower solids loading slurries. Zirconia balls were used

as the milling media and the mill jars are made of Alumina. But, due to losses in the

slurry suspension by using the ball mill, the misonix sonicator was used.









Misonix Sonicator 3000

For high solids loading slurries, the misonix sonicator 3000 ultrasonic horn was

used for the suspension preparation. The generator provides high voltage energy pulses at

20 kHz and takes care of the changes in the load conditions such as viscosity and

temperature. A titanium disruptor horn transmits and focuses oscillations of the

piezoelectric crystals and causes radiation of energy which under a phenomenon called

cavitationn" (formation and destruction of the microscopic vapor bubbles that the sound

waves generate) produces the shearing and tearing action necessary for the slurry

formation.

Suspension Preparation

Measured amounts of decahydronapthalene and the polymer (polystyrene or

polybutadiene or LP1) are taken in a beaker and placed on a hot stirrer till the polymer

dissolves in the carrier. This is followed by the addition of measured amounts of CCA7

and the product is placed in a misonix sonicator 3000 ultrasonic horn for 60 minutes. SiC

is then added. The product is then placed in misonix sonicator 3000 ultrasonic precursor

for 120 minutes. The suspension is thus prepared. This procedure is used for making

slurries to determine the optimum amounts of the polymer, charge controlling agent

required and for making slurries with different solids loading

Rheometer

Viscosity measurements were performed using a modular compact rheometer

(MCR 300, Paar Physica) with a concentric cylinder system using the US200 universal

software. The inner cylinder diameter is 27 mm. The temperature unit features peltier

heating.









Viscosity Measurements

The shear flow measurements are operated at 298K. The shear rate changes from

0.001 to 1000 s-1. The temperature control unit is TEZ150P, which features peltier

heating. The slurry is pre-sheared at 800s-1 for 60 seconds. The slurry is then kept

stationary for 10 seconds to equilibrate. Then the measurements are carried out. The

relative viscosity is the ratio of the viscosity of the suspension to the viscosity of

decahydronapthalene, at the same temperature [15].

Optical Density Measurement Equipment Setup

The voltage measurements during the electrophoretic deposition are done using the

DC voltage source (1-5 kV, Matsusada). A glass container holds the slurry. A steel

electrode acts as the cathode and another as the anode. The gap between the electrodes is

6 cm. One of the electrodes is grounded and on the other a developing bias voltage is

applied. The optical density is the ratio of the deposited mass to the surface area and this

gives information on the darkness of the print [13, 31, 32 and 33]. The application of

voltage leads to the deposition of SiC particles on the electrode. By measuring the optical

density for different voltages and time, graphs are plot showing the variation of optical

density with voltage and time


















































Figure 6-6.Flowchart for the suspension preparation














CHAPTER 7
EFFECT OF POLYMER ADSORPTION ON RHEOLOGY AND SOLIDS LOADING
OF THE SUSPENSION

Determination of the Optimum Amount of Polymer

The amount of the polymer added to the suspension must be just enough so that it

covers the SiC surface completely. The addition of excess may cause an increase in the

viscosity and if less than the required amount is added, the repulsive forces are not strong

enough to overcome the van der Waals forces of attraction. When there is the addition of

the optimum amount of the polymer, the repulsive barrier potential is high enough to

overcome the attractive potential [14, 15 and 17]. The optimum amount is the lowest

point on the graph plot between the weight percent of dispersant and viscosity.

Optimum Amount of Polystyrene

The viscosity measurements were carried out for different weight percent of

polystyrene in 5 vol% SiC with decahydronapthalene as the solvent. The shear rate taken

for the measurement is 161s-1. It is assumed that the lowest point in the figure 7-1, when

there is the complete coverage of the silicon carbide particles, is at 0.4 wt% polystyrene.

Thus, for all further experiments the amount of polystyrene added was fixed at this value.

Optimum Amount of LP1

Viscosity measurements were carried out for different weight percent of LP in 5

vol% SiC with decahydronapthalene as the solvent. The shear rate taken for the

measurement is 99.9s-1. It is assumed that the lowest point in the figure 7-2, when there is










the complete coverage of the silicon carbide particles, is at 0.4 wt% LP1. Thus, for all

further experiments the amount of LP1 added was fixed at this value.


0.03-


0.025


0.02-


. 0.015
-I


0.01-


0.005


0'


-- PS Shear rate 161 1/s


0 0.2 0.4 0.6 0.8 1
Wt % dispersant


Figure 7-1.Optimum amount of polystyrene required for complete coverage of the SiC
surface. The shear rate is 161s-1

Optimum Amount of Polybutadiene

The viscosity measurements were carried out for the different weight percent of

polybutadiene in 5 vol% SiC with decahydronapthalene as the solvent. The shear rate

taken for the measurement is 99.9s-1. It is assumed that the lowest point on the figure 7-3,

when there is the complete coverage of the silicon carbide particles, is at 0.4 wt%

polybutadiene. Thus, for all further experiments the amount of polybutadiene added was

fixed at this value.
















0.014


0.012


0.01


S0.008-


I 0.006


0.004


0.002




0 0.2 0.4 0.6 0.8 1

Wt % dispersant


Figure 7-2.Optimum amount ofLP1 required for complete coverage of the SiC surface.
The shear rate is 99.9s1.


0.007


0.006


0.005


& 0.004-


I 0.003


0.002


0.001 *


A PR hpar ratr p 99Q 1/I


0 0.2 0.4 0.6 0.8 1
Wt % dispersant


Figure 7-3.Optimum amount of polybutadiene required for complete coverage of the SiC
surface. The shear rate is 99.9s1.











Comparison of the Optimum Amounts of Dispersants

The variation of viscosity with different weight percent of polystyrene,

polybutadiene and LP1 in 5 vol% SiC with decahydronapthalene as the solvent is shown

in figure 7-4. It can be seen that the optimum amount for polystyrene, polybutadiene and

LP1 are 0.4, 0.3 and 0.4 wt% SiC respectively. Therefore, with the addition of the

optimum amount of the polymer, the repulsive barrier potential is high enough to

overcome the attractive potential and the complete coverage of the SiC particles is

obtained.





003


0025


002

S4 4--A LP1 Shear rate 99 9 1/s
0 0015 -B PS Shear rate 161 1/s
C PB Shear rate 99 9 1/s


001


0005



0 01 02 03 04 05 06 07 08 09
Wt % dispersant


Figure 7-4.5 vol% SiC in decahydronapthalene with varying amounts of the dispersants
polystyrene(PS), polybutadiene(PB) and LP1 used.

Determination of the Optimum Amount of Charge Controlling Agent

In industrial systems, the particle charging agents are added to control the

magnitude and the sign of the charge, for better dispersability and to adjust the









triboelectrically generated charge of the toner [18]. The optimum amount of the charge

controlling agent added to the suspension is the minimum amount that must be added to

get the highest amount of uniform deposition.

Optimum Amount of CCA7 in the LP1 suspension

In figure 7-5, there is an increase in the optical density with the addition of CCA7

for the slurry with the LP1 polymer and after further addition of CCA7 this value

decreases. It is seen, that the maximum optical density and therefore the optimum amount

of CCA7 is seen when the amount of CCA7 is 0.1 times the amount of polymer added. 5

vol% SiC in decahydronapthalene was used for the experiments. The time (sec)

mentioned for which the deposition was done was 60 seconds and the DC voltage applied

was +4kV. The amount of LP1 polymer added was 0.4 wt% SiC.

Optimum amount of CCA7 in the Polystyrene Suspension

In the figure 7-6 there is a decrease in the optical density with the addition of

CCA7 for the slurry with polystyrene and after further addition of CCA7 this value

increases. It is seen, that the maximum optical density and therefore the optimum amount

of CCA7 is seen when the amount of CCA7 is 0.1 times the amount of polymer added. 5

vol% SiC in decahydronapthalene was used for the experiments. The time (sec)

mentioned for which the deposition was done was 60 seconds and the DC voltage applied

was +4kV. The amount of polystyrene (PS) added was 0.4 wt% SiC. Therefore, for

polystyrene, the optimum amount of CCA7 is taken as 0.1 times the amount of the

polymer, as in this case the best deposition and maximum optical density is obtained.














0 16


0 14

012


S01

3 008

006


004


002

0
-3 5 -3 -25 -2 -1 5 -1 -05 0
Log (Amt of CCA7 wrt Amt of polymer added)




Figure 7-5.The amount ofLP1 added is 0.4 wt% SiC for the 5 vol% SiC in
decahydronapthalene. The deposition was done for 60 seconds and the DC
voltage applied was +4kV.

Comparison of the Optimum Amounts of CCA

From figure 7-7, the optimum amount of CCA7 is taken as 0.1 times the amount of


the LP1 polymer or polystyrene added as in this case we get the best deposition and the


maximum optical density. The optimum amount of the charge controlling agent added to


the suspension is the minimum amount that must be added to get the highest amount of


uniform deposition and the maximum optical density.


















009.


008*


007,


S006.


005,


004,


' 003


002.


001


0[


-35 -3 -25 -2 -1 5 -1

Log (Amt of CCA7 wrt Amt of polymer added)


Figure 7-6.The amount of polystyrene added is 0.4 wt% SiC for the 5 vol% SiC in

decahydronapthalene. The deposition was done for 60 seconds and the DC

voltage applied was +4kV.


A PS, 4 kV, 60 sec
|1B LP1, 4kV, 60 sec


0 1
-35 -3 -25 -2 -15 -1 -05 0
Log (Amount of CCA7 with respect to amount of polymer added)


Figure 7-7.The amount of LP1 and polystyrene(PS) added are 0.4 wt% SiC for the 5

vol% SiC in decahydronapthalene. The deposition time was 60 seconds and

the DC voltage applied was +4kV


-05 0


014


012


01


'" 008


S006
'.

004


002
















CHAPTER 8
EFFECT OF RELATIVE VISCOSITY ON SOLIDS LOADING OF THE NON POLAR
SILICON CARBIDE SUSPENSION

The viscosity of the slurry depends on the solids loading and this value reaches

infinity at the maximum volume fraction (Dm). The maximum volume fraction depends

on the particle size and the particle shape. At the maximum volume fraction, the particles

in the slurry are so close together that their average separation distance is almost zero and

this makes their flow impossible [14,16]. The experimental points have been fit to the

modified Krieger-Dougherty [16] equation.

For a SiC slurry in decahydronapthalene, the variation of shear rate with shear

stress shows a shear thinning behavior (figure 8-1).


100





10-











0.1
0.1 1 10 100 1000 10000
Shear Rate (s )


Figure 8-1.The variation of shear stress with shear rate for a 0.4 wt% LP1 stabilized
slurry with 5 vol% SiC in decahydronapthalene.











It is seen that with an increase in the shear rate there is also an increase in the shear

stress following the curve for the shear thinning behavior.The variation of shear rate with

viscosity, for a SiC slurry in decahydronapthalene, shows a shear thinning behavior

(figure 8-2). It is seen that with an increase in the shear rate there is a decrease in the

viscosity of the slurry.


10












0.1






0.01 1 1
0.1 1 10 100 1000 10000
Shear Rate (s 1)


Figure 8-2.The variation of shear stress with viscosity for a 0.4 wt% LP1 stabilized slurry
with 5 vol% SiC in decahydronapthalene.

Relative Viscosity on Solids Loading for the Polybutadiene Stabilized Suspension

From the figure 8-3, the graph between the volume fractions of silicon carbide with

respect to the relative viscosity, the maximum solids loading, Om, for the polybutadiene

suspension is found to be 0.69 (f =5.24). The higher Pm value illustrates that the packing









behavior is high in this case. The viscosity measurements were taken at a shear rate of

99.9s1

4000



3000



'12000



1000

OpI


10 20 30 40 50 60 70


Figure 8-3.Variation of relative viscosity with solids loading of SiC in
decahydronapthalene with 0.3 wt% SiC, being the polybutadiene (PB)
amount. The amount of CCA7 added was 0.1 times the amount of polymer
added to the slurry.

Relative Viscosity on Solids Loading Dependence for the LP1 Stabilized Suspension

From the figure 8-4, the graph between the volume fractions of silicon carbide with

respect to the relative viscosity, the maximum solids loading, Om, for the LP1 suspension

is found to be 0.55 [ r=5.4 ]. The higher (m value illustrates that the packing behavior is

high in this case. The viscosity measurements were taken at a shear rate of 99.9s-1






43



1400
If I

1200

1000
oI

o 800 ,

600

400

200


10 20 30 40 50 60


Figure 8-4.Variation of relative viscosity with solids loading of SiC in
decahydronapthalene with 0.4 wt% SiC, being the LP1 amount. The amount
of CCA7 added was 0.1 times the amount of polymer added to the slurry.

Solids Loading Dependence on Relative Viscosity for the Polystyrene Stabilized
Suspension

From the figure 8-5, the graph between the volume fraction of silicon carbide with

respect to the relative viscosity, the maximum solids loading, Om, for the polystyrene

suspension is found to be 0.22 ( q=12.8 ). The lower (m value illustrates that the packing

behavior is poor in this case. The viscosity measurements were taken at a shear rate of

99.9s-.










1200


1000 -


800

0 600

400

200


5 10 15 20 25


Figure 8-5.Variation of relative viscosity with solids loading of SiC in
decahydronapthalene with 0.4 wt% SiC, being the polystyrene (PS) amount.
The amount of CCA7 added was 0.1 times the amount of polymer added to
the slurry.

Comparison of the Stabilization Methods

The best fit of the experimental data shows that Om is drastically lower for the

suspension with polystyrene (0.22 [l=12.8]) compared to the LP1 suspension (0.55

[r=5.4]) or the polybutadiene suspension (0.69 [r =5.24]). We see that there is an

evident difference in the order of magnitude of the packing behaviour. The lower Pm

value illustrates that the packing behavior is poor in these cases. Therefore, the

polystyrene suspension will have a lower packing behavior than the polybutadiene and

LP1 polymer suspensions.










2000
II I

1750 I I






01000
I I
I I
II I








500 /
'I I
II I





250




10 20 30 40 50 60 70



Figure 8-6.Variation of relative viscosity with solids loading of SiC in
decahydronapthalene with 0.4 wt% SiC, being the LP1 and polystyrene (PS)
amounts and 0.3 wt% SiC the polybutadiene (PB) amount.The amount of
CCA7 added was 0.1 times the amount of polymer added to the slurry
CCA7 added was 0.1 times the amount of polymer added to the slurry














CHAPTER 9
EFFECT OF OPTICAL DENSITY VARIANCE WITH VOLTAGE

The voltage measurements during the electrophoretic deposition are done using the

DC voltage source (1-5 kV, Matsusada). The optical density is the ratio of the deposited

mass to the surface area and this gives information on the darkness of the print [13, 28,

32, and 33]. The application of voltage leads to the deposition of SiC particles on the

electrode. By measuring the optical density for different voltages and times, the variation

of optical density with voltage were obtained

Optical Density Variance with Voltage for LP1

The variation of voltage with optical density, for a 5 vol% SiC in

decahydronapthalene suspension, with LP1 polymer used as the dispersant are seen in

figures 9-1, 9-2 and 9-3. From the trend line in the figures it can be seen that initially the

optical density increases rapidly with voltage and after a while it stabilizes and there is

not too much of an increment in the optical density with increase in voltage. This point

usually seen at +4kV gave the best uniform deposition and so can be considered as the

best region to have the experiments carried out at.

For figure 9-1, the deposition was done for 120 seconds with no charge controlling

agent. The optical density increases rapidly initially and then stabilizes as shown by the

trend line. It is seen that at voltages below 4kV, the deposition formed is not uniform.

The lowest voltage at which the uniform deposition is seen to be achieved at was +4kV.

Hence +4kV was used for the experiments as the best voltage to work with.














0.07


0.06


S0.05


0.04


0.03


0.02
0 0.02 } T


0.01 L



0 1000 2000 3000 4000 5000
Voltage (V )


Figure 9-1.Variation of optical density with voltage for a LP1 slurry without charge
controlling agents and with a deposition time of 120 seconds.

For figure 9-2, the deposition time was 60 seconds with the charge controlling

agent in the slurry. The optical density increases rapidly initially and then if we

extrapolate the graph it stabilizes as shown by the trend line. It is seen that at voltages

below +4kV, the deposition formed is not uniform. The lowest voltage at which the

uniform deposition is seen to be achieved was +4kV.














0.16

0.14

0.12

0.1

0.08

0.06

0.04

0.02 {


0 1000 2000 3000 4000 5000 6000
Voltage ( V)


Figure 9-2.Variation of optical density with voltage for a LP1 slurry with charge
controlling agent 7 and a deposition time of 60 seconds.

For figure 9-3, the deposition was done for 120 seconds with the charge controlling

agent. The optical density increases rapidly initially and then stabilizes at around +4kV as

shown by the trend line. The lowest voltage at which the uniform deposition is seen to be

achieved was +4kV. Hence +4kV was used for the experiments as the best voltage to

work with.













0.18

0.16

0.14

0.12

0.1

So0.08

Z. 0.06

0.04

0.02


0 1000 2000 3000 4000 5000 6000
Voltage (V)


Figure 9-3.Variation of optical density with voltage for a LP1 slurry with charge
controlling agents and with a deposition time of 120 seconds.

Optical Density Variance with Voltage for Polystyrene

Figures 9-4, 9-5 and 9-6 show the variation of voltage with optical density, for a 5

vol% SiC in decahydronapthalene suspension, with polystyrene used as the dispersant.

From the trend line in the figures it can be seen that initially the optical density increases

rapidly with voltage and after a while it stabilizes and there is not too much of an

increment in the optical density with increase in voltage. This point usually seen at +4kV

gave the best uniform deposition and so can be considered as the best region in which for

conducting the experiments.

For figure 9-4, the deposition was done for 60 seconds and no charge controlling

agent was used. The lowest voltage at which the uniform deposition is seen to be










achieved was +4kV. Hence +4kV was used for the experiments as the best voltage to

work with.





0.06


0.05


0.04


S0.03


Z. 0.02


0.01



0 1000 2000 3000 4000 5000 6000
Voltage ( V)


Figure 9-4.Variation of optical density with voltage for polystyrene slurry without charge
controlling agents and a deposition time of 60 seconds.

For figure 9-5, the deposition was done for 60 seconds with the charge controlling

agent. The optical density increases rapidly initially and then stabilizes as shown by the

trend line. It is seen that at voltages below +3kV, the deposition formed is not uniform.

The lowest voltage at which the uniform deposition is seen to be achieved was +4kV.

Hence +4kV was used for the experiments as the best voltage to work with.













0.08

0.07

0.06

0.05

0.04

S0.03

0.02

0.01

0 1
0 1000 2000 3000 4000 5000 6000
Voltage (V)


Figure 9-5.Variation of optical density with voltage for polystyrene slurry with charge
controlling agent 7 and a deposition time of 60 seconds.

For figure 9-6, the deposition was done for 120 seconds with the charge controlling

agent. The optical density increases initially and then stabilizes. It is seen that at voltages

below 4kV, the deposition formed is not uniform. The lowest voltage at which the

uniform deposition is seen to be achieved was +4kV. Hence +4kV was used for the

experiments as the best voltage to work with.

Comparison of Optical Density Variance with Voltage for LP1 and Polystyrene

Figure 9-7 shows the optical density variation of the LP1 and polystyrene slurries

with and without the addition of CCA7 at different voltages and times. It can be inferred

from the data that LP1 slurries are better than polystyrene slurries as they have a much

higher optical density at the same voltage. Therefore, better liquid toners can be made

using the LP1 slurries.













0.07

0.06

S0.05

0.04

0.03

0 0.02

0.01



0 1000 2000 3000 4000 5000 6000
Voltage (V)


Figure 9-6.Variation of optical density with voltage for polystyrene slurry with charge
controlling agent 7 and a deposition time of 120 seconds.

It can also be inferred from the figure that a higher optical density was obtained with the

presence of the charge controlling agent (comparing the trend lines for C and D with A

and B or comparing the trend line for H with F). It is also seen that, the greater the time

of deposition, the greater was the optical density (comparing the trend lines for C with D

and A with B). Also, there was deposition on the steel electrode with the LP1 slurries by

the application of a high positive voltage and there was no deposition on the application

of a negative voltage. A positive voltage was applied and a layer of SiC was made to

adhere to the electrode and by reversing the voltage this layer could be removed. This

property of the LP1 slurries can be used for electro-photographic solid freeform

fabrication, where the steel electrode would be the photoconductor drum for the printer.

However in the case of the polystyrene slurries the application of either a high positive








53



voltage or a high negative voltage led to the deposition of SiC particles onto the steel


electrode. Therefore, these polystyrene slurries cannot be used as a liquid toner as they do


not completely follow the adhesion-non adhesion behavior with the application of


alternating positive and negative voltages. A DC voltage of +4kV is good for the process


as a good uniform deposition was seen to take place at this voltage.





0 18, Voltage (V) Vs Optical Density ( g/ cm2)

0 16

0 14 E PS, 2 mn,W-CCA
TREND LINE FOR C
TREND LINE FOR D
.N 0 12
S-TREND LINE FOR A
S-TREND LINE FOR B
0 1 TREND LINE FOR H
I -TREND LINE FOR F
008 A LP1,2mmn W -CCA
B LP1, 1 mln,W-CCA
O 006 C LP1,2min, CCA
+ D LP1, 1 minCCA
004 S F PS 1 mln,W -CCA
+ + G PS, 2 min, CCA
02 H PS, 1 mn CCA


02
0 1000 2000 3000 4000 5000 6000
Voltage (V )



Figure 9-7.Variance of optical density with voltage for 5 vol% SiC in decalin with 0.4
wt% SiC being the LP1 and polystyrene (PS) amounts.CCA, stands for the
slurries in which 0.1 times the amounts of polymer of CCA7 was added to the
slurry. W-CCA stands for those slurries in which CCA7 was not added. The
time (min) mentioned are the time for which the deposition was done.














CHAPTER 10
EFFECT OF OPTICAL DENSITY VARIANCE WITH TIME

The voltage measurements during the electrophoretic deposition are done using the

DC voltage source (1-5 kV, Matsusada). The optical density is the ratio of the deposited

mass to the surface area and this gives information on the darkness of the print [13, 31,

32 and 33]. The application of voltage leads to the deposition of SiC particles on the

electrode. By measuring the optical density for different times and voltages, the variation

of optical density with time were plot.

Optical Density Variance with Time for LP1

The variation of time with optical density, for a 5 vol% SiC in

decahydronapthalene suspension, with LP1 polymer used as the dispersant are shown in

figures 10-1, 10-2 and 10-3. From the trend line in the figures it can be seen that there is a

linear increase in optical density increases with time.

For figure 10-1, the applied voltage was +2kV and no charge controlling agent was

used. The optical density increases linearly with time as shown by the trend line.

For figure 10-2, the applied voltage was +4kV with no charge controlling agent.

The variation of optical density with time is linear. Therefore with an increase in time

there is a higher optical density

For figure 10-3, the applied voltage was +2kV with the charge controlling agent

being in the slurry. A linear relationship is seen with the optical density and time as

shown by the trend line.
























0.1

0.08

0.06

0.04

0.02

0 iL
0 50 100 150 200 250 300 350
Time (sec)



Figure 10-1.Variation of optical density with time for a LP1 slurry without charge
controlling agents and a deposition voltage of +2kV.





0.14


0.12


0.1


S0.08


S0.06

O 0.04


0.02



0 50 100 150 200 250 300 350
Time (sec)



Figure 10-2.Variation of optical density with time for a LP1 slurry without charge
controlling agents and a deposition voltage of +4kV.













0.16

0.14

0.12

0.1

0.08-

.1 0.06

0.04

0.02


0 50 100 150 200 250 300 350
Time (sec)


Figure 10-3.Variation of optical density with time for a LP1 slurry with charge
controlling agent 7 and a deposition voltage of +2kV.

Optical Density Variance with Time for Polystyrene

Figures 10-4, 10-5 and 10-6 show the variation of time with optical density for a 5

vol% SiC in decahydronapthalene suspension, with LP1 polymer used as the dispersant.

From the trend line in the figures it can be seen that the optical density increases with an

increase in time.

For figure 10-4, the applied voltage was +4kV with no charge controlling agent. A

linear relationship between optical density and time is seen as shown by the trend line.

Therefore with an increase in time a better optical density can be obtained.

For figure 10-5, the applied voltage was +2kV with the charge controlling agent

being in the slurry. The optical density increases linearly with time as shown by the trend

line.
















0.07


0.06


p 0.05


0.04-
41
0.03


o 0.02,


0.01


0


0 50 100 150 200 250 300 350
Time (sec)



Figure 10-4.Variation of optical density with time for a polystyrene slurry without charge
controlling agents and a deposition voltage of +4kV.






0.06 1


0.05


0.04-


S0.03-


S0.02


0.01


0 50 100 150 200 250 300 350
Time (sec)



Figure 10-5.Variation of optical density with time for a polystyrene slurry with charge
controlling agent 7 and a deposition voltage of +2kV.





^*^"*v^^'


L


1











For figure 10-6, the applied voltage was +4kV with the charge controlling agent.


The trend line shows that a increase in optical density is obtained with time. Therefore

with longer duration for the deposition a higher optical density can be obtained.





0.07 i


0.06


- 0.05

04'
S0.04


Q 0.03'


S0.02


0.01


0.


0 50 100


0 200
Time (sec)


250 300


Figure 10-6.Variation of optical density with time for a polystyrene slurry with charge
controlling agent 7 and a deposition voltage of +4kV.

Comparison of Optical Density Variance with Time for LP1 and Polystyrene

Figure 10-7, shows the optical density variation of the LP1 and polystyrene slurries

with and without the addition of CCA7 at different times and voltages. It can be inferred

from the data that LP1 slurries are better than polystyrene slurries as they have a much

higher optical density as compared to polystyrene slurry for the same time of deposition.

Therefore, better liquid toners can be made using the LP1 slurries. It can also be seen,

from the figure, that a higher voltage gave a higher optical density (comparing the trend

lines for E and F) and similarly the presence of CCA7 increases the optical density


_


L


L








59



(comparing B with C and G with E). It's also seen that with an increase in time there is a


better optical density and this follows a linear relationship. For liquid toner applications a


higher optical density in a minimum time of deposition is needed. So it can be seen that


the LP1 slurry can be used as a liquid toner. It was seen, during the experiments that the


uniformity in the deposition on the electrode occurred at voltages around +4kV. So most


of the experiments were carried out at +4kV.






0 14


0121


*- U




++
++ +
+


* A LP1, 2kV, W-CCA
* B LP1, 4kV, W-CCA
C LP1, 2kV, CCA
D LP1, 4kV, CCA
X E PS, 2kV, W-CCA
F PS, 4kV, W-CCA
+ G PS, 2kV, CCA
H PS, 4kV, CCA
TREND LINE FOR D
TREND LINE FOR C
-TREND LINE FOR B
-TREND LINE FOR G
-TREND LINE FOR F
-TREND LINE FOR E


0 50 100 150 200 250 300 350
Time (sec)



Figure 10-7.The variation of optical density with time for a 5 vol% SiC in
decahydronapthalene with 0.4 wt% SiC being the LP1 and polystyrene (PS)
amounts. CCA, stands for the slurries in which 0.1 times the amounts of
polymer of CCA7 was added to the slurry. W-CCA stands for those slurries in
which CCA7 was not added. The voltages mentioned are the DC voltages for
which the deposition was done.


01.
E
U

. 008


m 006
.2
O
004


002














CHAPTER 11
ANALYSIS OF THE ELECTROPHORETIC DEPOSITION

For the electro-photographic solid freeform application, electrophoretic adhesion-

non adhesion tests were carried out to find out the best volume fraction to work with. For

the adhesion-non adhesion tests, the steel electrode was dipped into slurries with LP1,

polybutadiene and polystyrene as dispersants and at different solids loading of 5, 10, 15,

20, 30, 40, 50 and 60 vol% SiC. The aim was to work with the slurry, into which if the

electrode was dipped and kept for a certain period of time (60 seconds) and taken out, did

not have any SiC particles deposited. The long term application being that the electrode

could be used as the photoconductor drum in the printer. It was found that at lower

volume fractions this adhesion-non adhesion behavior was seen better and for slurries

with polystyrene and LP1, a perfect example of this was seen at 5 vol% SiC. So, further

experiments were carried out with 5 vol% SiC. Polybutadiene slurries did not make a

favorable response to the adhesion-non adhesion tests and so were not considered for

making a liquid toner.

Since LP1 and polystyrene satisfied the first set of experiments. The next test was

to place the electrode in the slurry and to apply a voltage on the electrode for 60 seconds.

The electrode was then taken out of the suspension. The aim of the experiment was to see

if a layer of silicon carbide was deposited on the electrode or not. It was seen that both

polystyrene and LP1 satisfied these tests.

The final experiment was to place the electrode in the slurry, apply a voltage,

reverse the voltage and see if most of the deposition could be taken off from the









electrode. For the LP1 slurries there was deposition on the steel electrode by the

application of a high positive voltage and there was no deposition on the application of a

negative voltage. A positive voltage was applied and a layer of SiC was made to adhere

to the electrode and by reversing the voltage this layer could be removed. This property

of the LP1 slurries can be used for electro-photographic solid freeform fabrication, where

the steel electrode would be the photoconductor drum for the printer. However in the case

of the polystyrene slurries the application of either a high positive voltage or a high

negative voltage led to the deposition of SiC particles onto the steel electrode. Therefore,

these polystyrene slurries cannot be used as a liquid toner as they don't completely follow

the adhesion-non adhesion behavior with the application of alternating positive and

negative voltages. A DC voltage of +4kV is good for the process as a good uniform

deposition was seen to take place at this voltage.

Scanning Electron Microscope Images

Polystyrene Samples

The SEM images of the deposited layer with the suspension of 5vol% SiC in

decahydronapthalene with polystyrene is seen in figure 11-1. A voltage of +4kV was

applied for 60 seconds. The SEM image was taken at a magnification of 20,000X with a

working distance of 13.3mm.

The SEM images of the deposited layers with the suspension of 5vol% SiC in

decahydronapthalene with polystyrene and the charge controlling agent, CCA7 is seen in

figure 11-2. A voltage +4kV was applied for 60 seconds. The SEM image was taken at a

magnification of 20,000X and a working distance of 14.3mm.






























Figure 11-1.SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension
in decahydronapthalene with polystyrene.


Figure 11-2.SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension
in decahydronapthalene with polystyrene and the charge controlling agent 7.









LP1 Samples

The SEM images of the deposited layer with the suspension of 5vol% SiC in

decahydronapthalene with LP1 is seen in figure 11-3. A voltage of +4kV was applied for

60 seconds. The SEM image was taken at a magnification of 10,000X with a working

distance of 15.5mm.


Figure 11-3.SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension
in decahydronapthalene with LP1 polymer.

The SEM image of the deposited layers with the suspension of 5vol% SiC in

decahydronapthalene with LP1 and the charge controlling agent, CCA7 is seen in figure









11-4. A voltage of +4kV was applied for 60 seconds. The SEM image was taken at a

magnification of 10,000X with a working distance of 13.4mm.


Figure 11-4.SEM of the electrophoretic deposit formed from the 5 vol% SiC suspension
in decahydronapthalene with LP1 polymer and the charge controlling agent 7.

Digital Camera Pictures

Digital camera pictures of the electrophoretic deposition done were taken and are

seen in figures 11-5, 11-6, 11-7, 11-8 and 11-9. Figure 11-5 is a picture taken after the

steel electrode was dipped into a 5vol% SiC in decahydronapthalene with the LP1

polymer suspension for 60 seconds. There was no voltage applied. We see that there is no

layer formed on the electrode. Therefore, this slurry satisfied the first test A slurry into









which if the electrode was dipped and kept for a certain time and then taken out did not

have any SiC particles adhered to it.

























Figure 11-5.Digital camera picture of the steel electrode after it was dipped into the 5
vol% SiC in decahydronapthalene with LP1 polymer suspension and kept for
60 seconds without the application of a voltage.

Figure 11-6 is a digital camera picture of a steel electrode after it was dipped in the

5 vol% SiC in decahydronapthalene with the LP1 polymer suspension for 60 seconds.

The voltage applied was +4kV. We see that there is a uniform layer formed on the

electrode. Therefore, this slurry satisfied the second test A slurry into which if the

electrode was dipped and kept for a certain time, at a particular voltage and then taken

out had SiC particles adhered to it.

Figure 11-7 shows a picture taken after the steel electrode was dipped into a 5 vol%

SiC in decahydronapthalene with the polystyrene polymer suspension for 60 seconds.

There was no voltage applied. We see that there is no layer formed on the electrode.









Therefore, this slurry satisfied the first test A slurry into which if the electrode was

dipped and kept for a certain time and then taken out did not have any SiC particles

adhered to it.


Figure 1 1-6.Digital camera picture of the steel electrode after it was dipped into the 5
vol% SiC in decahydronapthalene suspension with LP1 polymer and kept for
60 seconds with the application of a voltage of +4kV


Figure 1 1-7.Digital camera picture of the steel electrode after it was dipped into the 5
vol% SiC in decahydronapthalene suspension with the polystyrene polymer
and kept for 60 seconds without the application of a voltage






67


Figure 11-8 and 11-9 are digital camera pictures of the steel electrode after it was

dipped in the 5 vol% SiC in decahydronapthalene suspension with the LP1 polymer. A

voltage of +4kV was applied for 60 seconds and then the voltage was reversed to -4kV

for 60 seconds. We see that there is hardly any of the SiC deposit left on the electrode.

Therefore, this slurry satisfied the third test A slurry into which if the electrode was

dipped and kept for a certain time, for a particular voltage and then reversing the voltage

and keeping it for the same amount of time and when taken out had no SiC particles

adhered to it.





















































Figure 11-8 and 1 1-9.Digital camera picture of the steel electrode after it was dipped into
the 5 vol% SiC in decahydronapthalene suspension with LP1 polymer and
kept for 60 seconds with the application of +4kV and for another 60 seconds
with the application of -4kV.














CHAPTER 12
CONCLUSION

The optimum amounts for polystyrene, polybutadiene and LP1 polymers are 0.4,

0.3 and 0.4 wt% SiC respectively. The maximum optical density and therefore the

optimum amount of Charge Controlling Agent (CCA7) is when the amount of CCA7 is

0.1 times the amount of polystyrene or LP1 added to the slurry. All slurries are shear

thinning. The dependence of relative viscosity on solids loading is different for the

slurries with LP1, polybutadiene or polystyrene as the polymer. There is an order of

magnitude difference in the maximum solids loading between these slurries. The

maximum solids loading attainable (Om ) using the Krieger- Dougherty fit equation, for

the polystyrene slurry was 0.22 [rl=12.8]. For the LP1 slurry the maximum solids loading

(Om) was 0.55 [rl=5.4] and for the polybutadiene slurry ((Om) was 0.69 [rf =5.24]).

Lower solids loading indicate poor particle packing. Therefore, the packing density will

be higher for the polybutadiene slurries as compared to the LP1 and polystyrene slurries.

At lower volume fractions [5 vol % SiC] the electrophoretic adhesive-non adhesive

behavior was better for slurries with polystyrene and LP 1. Polybutadiene slurries did not

make a favorable response to the adhesive- non adhesive tests and so were considered

"not good" for making a liquid toner. Better deposition can be made using the LP1

slurries as they have a much higher optical density as compared to polystyrene slurry at

the same voltage. Polystyrene slurries cannot be used as a liquid toner as they don't

completely follow the adhesive- non adhesive behavior with the application of alternating

positive and negative voltages. A +4kV DC voltage was found to be sufficient for the






70


electrophoretic deposition process. There is a large increase in the optical density with the

addition of the CCA7 in the slurry. A linear dependence of optical density on deposition

time was established experimentally.















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[13] S. Matsumoto, K. Satou, J. Matsuno, A. Sasaki, T. Akasaki and K. Kamio,
Mechanism of Liquid Development Using Highly Concentrated Liquid Toner,
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California, (2002)

[14] M. N. Rahaman, Ceramic Processing and Sintering, Marcel Dekker Inc, New York
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[15] K. Sunita, Impact of Electric Double Layer and Electrosteric Stabilization
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BIOGRAPHICAL SKETCH

Navin was born on the 4th of July 1979, in Cochin, India-the queen of the Arabian

Sea. Being an outstanding student all though his academic career, he received

scholarships for his entire schooling. He is an amazing tennis player and was ranked in

the top hundred in singles and doubles in men's tennis in India (1997). He has even

participated and won prizes (1990-95) at the national level in enterprise class sailing and

water-skiing.

His first steps towards an engineering career came in May 1997 with his admission

into the prestigious Regional Engineering College (now called the National Institute of

Technology), Warangal, Andhra Pradesh, India-the oldest of the NITs. A consistently

high academic performance got him the "Naval Foundation" scholarship for his entire

undergraduate program in Metallurgical Engineering. He graduated from NIT, Warangal

with the "Alumni Association Gold Medal," for being the best outgoing student and all-

rounder and also the "Sri Kabadi Subalu Silver Medal," for being the best outgoing

sportsperson among the students graduating in the year 2001. The first student from NIT

Warangal since it was founded in 1959 to win two of these prestigious medals.

After graduation, a decision had to be made between joining Mahindra British

Telecomm (MBT), Pune, India, as a software engineer or to go in for higher studies. A

graduate research assistantship with Dr Wolfgang Sigmund in Materials Science and

Engineering at the University of Florida, Gainesville, made the decision easier. Ever

since, Navin has been here at Gainesville and will be graduating with a Master of Science






75


degree in May 2003. At Gainesville, he has continued to involve himself with the

international community and is presently the vice president of the Indian Student

Association (ISA) on campus, the largest ISA in the United States. He is also the Indian

representative to the Student Government (SG) and the Volunteers of International

Students Association (VISA) on campus.