Citation
Strategies for Enhancing the Mechanical Durability of Transparent Superhydrophobic Coating and Development of Color and Durable Superhydrophobic Paint

Material Information

Title:
Strategies for Enhancing the Mechanical Durability of Transparent Superhydrophobic Coating and Development of Color and Durable Superhydrophobic Paint
Creator:
Hung, Yung-Chieh
Publisher:
University of Florida
Publication Date:
Language:
English

Thesis/Dissertation Information

Degree:
Doctorate ( Ph.D.)
Degree Grantor:
University of Florida
Degree Disciplines:
Materials Science and Engineering
Committee Chair:
SIGMUND,WOLFGANG MICHAEL
Committee Co-Chair:
MECHOLSKY,JOHN J,JR
Committee Members:
WEBB,ANTONIO R
MYERS,MICHELE V
WU,CHANG-YU

Subjects

Subjects / Keywords:
antibiofouling
coating
nonwetting
selfcleaning
superhydrophobic
wearresistance

Notes

General Note:
Superhydrophobic surfaces feature repellency of liquids and enhance existing or enable novel technologies such as self-cleaning, have anti-fouling behavior, and ice phobicity. Superhydrophobicity is quantitatively described by surface science theories such as the Cassie Baxter model. From this model it is obvious that changes in the surface chemistry due to oxidation or surface topography due to abrasion or aging causes the coating to lose its superhydrophobic property. This lack of durability in products currently limits the commercial breakthrough of this technology. This dissertation addresses four major objectives. 1) Development of a quantitative durability test that could be standardized. 2) Develop a composite paint for durability. 3) Understand the structure of durable superhydrophobic coatings. 4) Apply this knowledge to build the ultimate coating which is superhydrophobic, durable and transparent. Such a coating could be applied to any material or device without changing its looks and is most desired by a large number of companies throughout the world. This dissertation addresses the above mentioned challenges first by developing and testing and applying a new wear resistance measurement approach for superhydrophobic coatings, which could be used for standardization in this field. It is built on existing ASTM standards with modification for superhydrophobic surfaces. Moreover, the advances achieved by using this standard for characterizing samples allowed the development of novel superhydrophobic coatings that are durable. The concept that was applied is based on funicular and pendular structures in mostly dense composite materials consisting of hydrophobic polymers with hydrophobic ceramic particles. The volumetric thick thermoplastic component of the paint layer gives the mechanical strength to achieve superhydrophobicity through 1000 abrasion cycles by metallurgy sand paper and 12 days of a UV exposure. The scalability was addressed by formulating this coating as a paint. This allows for application to large areas, and the possibility to add color beyond white, which in this work is black, blue, green and red. The concept allows to fabricate any other type of color paint as long as the pigments can be hydrophobized or are themselves already hydrophobic. The system is based on a polymethyl methacrylate-polyvinylidene difluoride (PMMA-PVDF) polymer blend, acting as a thermoplastic binder, and hydrophobized metal oxides particles, which develop surface roughness. Coatings were applied to glass surfaces as well as pre-painted surfaces. Wettability, wear index, and coating degradation rate (CDR) are reported. The application of this breakthrough to transparent SH coatings is of course more challenging. Such transparent superhydrophobic coating could for example be applied on solar cell panels to keep them clean and at their highest efficiency. Cars would not need to be washed as long as it rains sometimes and operating rooms and hospitals overall could be kept at lower number of bacteria, viruses and dust by such coatings. Several reports exist that demonstrated transparent superhydrophobic coatings using nanoparticles that are below the Fraunhofer and Mie scattering for light. However, all these coatings suffer from lack of durability. This is due the oxidation of the materials and the low thickness of the coating. In order to achieve durable and transparent SH coating, novel approaches are reported in this dissertation. Moving from an organic-inorganic paint system to a ceramic-ceramic system allows to reduce scattering coming from the variation in refractive indices of the components. A sol-gel cover layer is used to enhance mechanical and chemical bonding of nanoparticles. All of these materials can be kept below the scattering limits for visible light. After fluorination, a transparent and superhydrophobic coating was achieved. Moreover, a second novel concept using particle agglomeration and bonding to enhance transparent superhydrophobic material is introduced. Monodisperse silica nanoparticles were treated with a variety of silane coupling agents. By doing so, the silica nanoparticles became functionalized with reactive groups that allowed bonding under specific conditions. The introduction of directly chemically bonding particles further enhanced the durability. However, more needs to be done since the scattering limits of the materials in composites or just the surface features alone make it challenging to provide the proper surface architecture and chemistry while being mechanically robust to withstand abuse. In summary this work advances the field of superhydrophobic coatings, applies the theories and standards for characterization, and demonstrates them in examples of novel durable ceramic-polymer and transparent ceramic-ceramic composite coatings.

Record Information

Source Institution:
UFRGP
Rights Management:
All applicable rights reserved by the source institution and holding location.
Embargo Date:
8/31/2018

Downloads

This item has the following downloads:


Full Text

PAGE 1

STRATEGIES FOR ENHANCING THE MECHANICAL DURABILITY OF TRANSPARENT SUPERHYDROPHOBIC COATING AND DEVELOPMENT OF COLOR AND DURABLE SUPERHYDROPHOBIC PAINT By YUNG CHIEH HUNG A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2016

PAGE 2

2016 Yung Chieh Hung

PAGE 3

To the family and friends that helped me make it th rough

PAGE 4

4 ACKNOWLEDGMENTS I would like to thank my advisor Dr. Sigmund and the members of Sigmund group. We learned new things by brainstorming every day that I have spent here on University of Florida. I also would like to thank my parents and my wife bec ause they always encourage d me when I was down Without their assistance, I may not have been able to make it through.

PAGE 5

5 TABLE OF CONTENTS Page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 4 LIST OF TABLES ................................ ................................ ................................ ........................... 9 LIST OF FIGURES ................................ ................................ ................................ ....................... 10 LIST OF ABBREVIATIONS ................................ ................................ ................................ ........ 14 ABSTRACT ................................ ................................ ................................ ................................ ... 15 CHAPTER 1 SUPERHYDROPHOBIC AND HYDROPHOBIC MATERIALS ................................ ........ 18 Introduction ................................ ................................ ................................ ............................. 18 Wetting Theory ................................ ................................ ................................ ....................... 19 Surface Tension ................................ ................................ ................................ ............... 19 Wetting Equilibria ................................ ................................ ................................ ........... 19 Contact Angle ................................ ................................ ................................ .................. 20 Classical Models for Co ntact Angles on Rough Surfaces Wenzel State ........................ 2 1 Heterogeneous Solid Liquid Interface: Cassie Baxter Model ................................ ........ 22 Contact Angle Hysteresis ................................ ................................ ................................ 23 Transition between Cassie Baxter and Wenzel State ................................ ...................... 24 Contact Angle Measurement ................................ ................................ ................................ .. 25 Traditional Superhydrophobic Surface Fabrication ................................ ................................ 26 Making Hairy Surface via Moulding Techniques: ................................ .......................... 26 Casting Fine Surface Structure via Photolithography ................................ ..................... 27 Current Limitations of Superhydrophobic Materials ................................ .............................. 28 Mechanical Durability ................................ ................................ ................................ ..... 28 Optical Property ................................ ................................ ................................ ............... 29 Current Measurements for Mechanical Durability of Superhydrophobic Surface ................. 29 Chapter Summary ................................ ................................ ................................ ................... 30 2 FABRICATION OF DURABLE AND SUPERHYDROPHOBIC PAINT WITH COMMERCIAL FLUORO POLYMER ................................ ................................ ................ 32 Introduction ................................ ................................ ................................ ............................. 32 Standardize Wear Resistance Test for Superhydrophobic Coating/ Material ........................ 32 Measurement of Water Contact Angle Change against Abrasion Cycles ....................... 33 Measurement of Weight Loss against Abrasion Cycles ................................ .................. 34 Novel Design Perspective of Durable Superhydrophobic Coating ................................ ........ 34 Stacking of Granular Material ................................ ................................ ................................ 35 Particles and Polymer Selection ................................ ................................ ............................. 36

PAGE 6

6 Fabrication of Water Borne Superhydrophobic and Durable Coating with Commercial Fluoro Polymer ................................ ................................ ................................ ................... 37 Materials and Ex perimental Process ................................ ................................ ............... 37 Fabrication of superhydrophobic white pigments ................................ .................... 37 Preparation of coating samples with different V% ................................ .................. 37 Sample preparation ................................ ................................ ................................ ... 38 Method of measurement ................................ ................................ ........................... 38 Results and Discussio n ................................ ................................ ................................ ........... 38 Initial Contact Angle of White Coating with Different V% Pigments Adding ............... 38 Abrasion Test with 1200P Sandpaper as Abrader Lumiflon White Paint System ........ 40 Summary ................................ ................................ ................................ ................................ 41 3 FABRICATION OF DURABLE AND SUPERHYDROPHOBIC COLOR PAINTS .......... 43 Introduction ................................ ................................ ................................ ............................. 43 Superhydrophobic White Paint Fabrication and Characterization ................................ ......... 44 Materi als and Experimental Process ................................ ................................ ............... 44 Fabrication of superhydrophobic white pigments ................................ .................... 44 Binder blending ................................ ................................ ................................ ........ 44 Preparation of coating samples with different V% ................................ ................. 44 Method used for measurement ................................ ................................ ................. 45 Results and Discussion ................................ ................................ ................................ ........... 45 Initial Contact Angle Measurement ................................ ................................ ................. 45 Contact Angle Change with Abrasion Test ................................ ................................ ..... 46 Wear Index and CDR Calculation ................................ ................................ ................... 47 SEM Characterization ................................ ................................ ................................ ..... 48 Discussion and Understanding ................................ ................................ ............................... 51 Summary ................................ ................................ ................................ ................................ 52 Superhydrophobic Black Paint Fabrication and Characterization ................................ .......... 53 Materials and Experimental Process ................................ ................................ ............... 53 Fabrication of superhydrophobic black pigments ................................ .................... 53 Binder blending ................................ ................................ ................................ ........ 53 Preparation of coating samples with different V% ................................ .................. 53 Results and Discussion ................................ ................................ ................................ ........... 54 Initial Contact Angle Measurement ................................ ................................ ................. 54 Black Paint Wear Resistance Test by Using 1200C Sand Paper as Abrader .................. 55 Black Paint Wear Resistance Test by Using 600 C Sandpaper as Abrader .................... 57 Summary ................................ ................................ ................................ ................................ 59 Superhydrophobic Blue Paint Fabrication and Characterization ................................ ............ 60 Materials and Experimental Process ................................ ................................ ............... 60 Fabrication of superhydrophobic blue pigments ................................ ...................... 60 Binder blending ................................ ................................ ................................ ........ 60 Preparation of pure blue coating samples with different V% ................................ .. 60 Preparation of white blue mixed paint ................................ ................................ ..... 60 Results and Discussion ................................ ................................ ................................ ........... 61 Initial Contact Angel Measurement ................................ ................................ ................. 61 Wear Resistance Test by Using 600C Sand Paper Blue Paint ................................ ...... 61

PAGE 7

7 White Paint Blended by Blue Pigments ................................ ................................ .......... 64 Summary ................................ ................................ ................................ ................................ 65 Superhydrophobic Green Paint Fabrication and Characterization ................................ ......... 66 Materials and Experimental Process ................................ ................................ ............... 66 Fabrication of superhydrophobic green pigments ................................ .................... 66 Binder blending ................................ ................................ ................................ ........ 66 Preparation of pu re green coating samples with different V% ................................ 66 Preparation of white green mixed paint ................................ ................................ ... 66 Initial Contact Angle of Coating with Di fferent V% Pigments ................................ ...... 67 Wear Resistance Test by Using 600C Sand Paper Green Paint ................................ .... 67 White Paint Blended by Green Pigments ................................ ................................ ........ 69 Summary ................................ ................................ ................................ ................................ 71 Superhydrophobic Red Paint Fabrication and Characterization ................................ ............. 71 Materials and Methods ................................ ................................ ................................ .... 71 Fabrication of superhydrophobic red pigments ................................ ........................ 71 Binder blending ................................ ................................ ................................ ........ 72 Preparation of pure red coating samples with different V% ................................ .... 72 Preparation of white red mixed paint ................................ ................................ ....... 72 Results and Discussion ................................ ................................ ................................ ........... 72 Initial Contact Angle Measurements Red Paint ................................ ............................. 72 Abrasion Test by Using 600c Sand Paper Red Paint ................................ ................... 73 White Paint Blended by Red Pigments ................................ ................................ ........... 75 Summary ................................ ................................ ................................ ................................ 76 Disc ussion and Understanding ................................ ................................ ............................... 77 Chapter Conclusion ................................ ................................ ................................ ................ 78 4 FABRICATION OF DURABLE SUPERHYDROPHOBIC AND TRANSPARENT COATING VIA SILICA S OL GEL COVER LAYER ................................ .......................... 80 Introduction ................................ ................................ ................................ ............................. 80 Background ................................ ................................ ................................ ............................. 80 Light Scatte ring Theory ................................ ................................ ................................ ... 80 Silica Nanoparticles Synthesis via Stber Process ................................ .......................... 81 pH Dependence ................................ ................................ ................................ ...... 83 Polymerization above ph7 ................................ ................................ ........................ 83 Fundamental of Sol Gel Dip Coating ................................ ................................ .............. 84 Materials and Methods ................................ ................................ ................................ ........... 85 Silica nanoparticles synthesis (stber process) ................................ ........................ 85 Silica sol gel synthesis ................................ ................................ ............................. 85 Silica nanoparticles deposition ................................ ................................ ................. 85 Silica sol gel deposition ................................ ................................ ........................... 86 Self assembled monolayer deposition hydrophobization ................................ ........ 86 Results and Discussion ................................ ................................ ................................ ........... 86 Initial Contact Angle Measurement ................................ ................................ ................. 86 Contact A ngle Change against Abrasion Cycles ................................ ............................. 87 Transmittance Measurement ................................ ................................ ........................... 88 Summary ................................ ................................ ................................ ................................ 89

PAGE 8

8 5 FABRICATION OF DURABLE SUPERHYDROPHOBIC AND TRANSPARENT COATING VIA SILANE COUPLING AGENTS ................................ ................................ 90 Introduction ................................ ................................ ................................ ............................. 90 B ackground ................................ ................................ ................................ ............................. 91 Silane Coupling Agents ................................ ................................ ................................ ... 91 Strategy to Bond Nanoparticles and Glass Surface ................................ ......................... 92 Thiol disulfide reaction ................................ ................................ ............................ 93 Conjugation of thiol group after oxidation ................................ ............................... 93 Materials and Methods ................................ ................................ ................................ .... 94 Silica nanoparticles synthesis (Stber process) ................................ ........................ 94 Preparation of thiol terminated silica nanoparticles ................................ ................. 94 Preparation of thiol terminated glass slide ................................ ............................... 94 Deposit T particles on T glass ................................ ................................ ................. 95 Thiol disulfide oxidation ................................ ................................ .......................... 95 Hydrophobization ................................ ................................ ................................ ..... 95 Results and Discussion ................................ ................................ ................................ ........... 95 Wear Resistance of Samples with Different Oxidation Condition ................................ .. 95 Summary ................................ ................................ ................................ ................................ 97 6 CONCLUSION ................................ ................................ ................................ ....................... 98 LIST OF REFERENCES ................................ ................................ ................................ ............. 100 BIOGRAPHICAL SKETCH ................................ ................................ ................................ ....... 106

PAGE 9

9 LIST OF TABLES Table page 1 1 Current methods to measure wear resistance of SH material ................................ ............ 29 1 2 Current methods to characterize wear resistance of SH material ................................ ...... 30

PAGE 10

10 LIS T OF FIGURES Figure page 1 1 Spreading wetting ................................ ................................ ................................ .............. 19 1 2 Contact angle ................................ ................................ ................................ ..................... 20 1 3 Wetting behavior of a liquid droplet on solid surface and their mathematical models. .... 23 1 4 Contact angle hysteresis. ................................ ................................ ................................ .... 24 1 5 Image of contact angle measurement. ................................ ................................ ................ 25 1 6 Commercial polycarbonate membrane with pore size 3m ................................ .............. 27 1 7 Fabrica tion of superhydrophobic from polypropylene. ................................ ..................... 27 1 8 Superhydrophobic hairy polypropylene surface. ................................ ............................... 28 2 1 Difference of tradition al design and new design. ................................ .............................. 35 2 2 Schematic of final dried material with different particle polymer ratio ............................ 36 2 3 Chemical structu re of Lumiflon 4400 from Asahi ................................ ............................. 37 2 4 Higher volume percent of fluorinated silica adding turns out higher initial contact angle ................................ ................................ ................................ ................................ ... 39 2 5 Scheme of polymer distribution status with different volume percent in particle binder composite ................................ ................................ ................................ ................ 39 2 6 Water contact angle change against abrasion cycles Lumiflon white paint system ....... 40 2 7 Weight change against abrasion cycles Lumiflon white paint system ........................... 41 3 1 Higher pigment V% yields higher initial contac t angle white paint ................................ 45 3 2 Contact angle decreases with abrasion cycles increase white paint ................................ 46 3 3 List of slopes of the reg ression line of decreasing WCA white paint system ................... 47 3 4 Scheme of polymer distribution status with different volume percent in particle binder composite ................................ ................................ ................................ ................ 47 3 5 Weight loss with different volume percent after abrasion white paint ............................. 48 3 6 List of wear index, weight loss part per thousand, and slope of regression line fo r by varying the Volume percent of pigments adding ................................ ............................... 48

PAGE 11

11 3 7 Cross section of coating with 38.46V% of particle and the polymer distribution is in capillary stage. ................................ ................................ ................................ ................... 49 3 8 Cross section of coating with 55.85V% of particle ................................ ........................... 50 3 9 Cross section of coating with 61.08V% paint and the polymer distribution is in funicular stage ................................ ................................ ................................ .................... 50 3 10 Cross section of coating with 65.22V% paint and particles are bonded by polymer bridge and show s a flaky structure ................................ ................................ ..................... 50 3 1 1 Calculated roughness factor ( ) of surfaces with packing density 74% and 52% ............. 51 3 12 Calculated solid fraction ( ) and roughness factor ( ) ................................ .................... 51 3 13 Initial contact angle of black paint with different V% black paint ................................ ... 54 3 14 Contact angle changes against abrasion cycles increase black paint/ 1200C sand paper ................................ ................................ ................................ ................................ ... 55 3 15 List of contact angle trend black paint/ 1200C sand paper ................................ .............. 55 3 16 Weight loss with different volume percent after abrasi on black paint ............................. 56 3 17 List of wear index, weight loss part per thousand, and slope of regression line for by varying the volume percent of pigments adding black paint/ 1200C sand paper ............. 56 3 18 Contact angle fluctuate with abrasion cycles increase black paint/ 600C sand paper ...... 57 3 19 Contact angle declining trend b lack paint / 600C sand paper ................................ .......... 58 3 20 Weight loss with different volume percent after abrasion black paint/ 600C sand paper ................................ ................................ ................................ ................................ ... 58 3 21 List of wear index, weight loss part per thousand, and slope of regression line for by varying the volume percent of pigments adding black paint/ 600C sand paper ............... 59 3 22 Initial contact an gle of blue paint with different V% ................................ ........................ 61 3 23 Contact angle decreases with abrasion cycles increase blue paint/ 600C sand paper ...... 62 3 24 Contact angle decreasing trend of blue paint/ 600C sand paper ................................ ....... 62 3 25 Weight change against abrasion cycles increase blue paint/ 600C sand paper ................. 63 3 26 List of wear index, weight loss (%) and slope of regression line for by varying the volume percent of pigments adding blue paint/ 600C sand paper ................................ ... 63 3 27 App earances of B1 to B 4 ................................ ................................ ................................ ... 64

PAGE 12

12 3 28 DI water contact angle for B1~B4 samples ................................ ................................ ....... 64 3 29 Change of contact angle with increasing of abrasio n cycles for white blue mixed paint system ................................ ................................ ................................ ....................... 65 3 30 Higher pigment volume percent yields higher initial contact angle green paint system ................................ ................................ ................................ ................................ 67 3 31 Contact angle fluctuates with abrasion cycles increase green paint/ 600C sand paper .... 68 3 32 Contact angle changing trend of green paint/ 600C sand paper ................................ ....... 68 3 33 Weight change in percentage against abrasion cycles increase green paint/ 600C sand paper ................................ ................................ ................................ .......................... 69 3 34 List of wear index, weight loss (%), and slope of regression line (CDR) for by varying the volume percent of pigments adding green paint/ 600C sand paper .............. 69 3 35 Appearances of G1 to G4 ................................ ................................ ................................ ... 70 3 36 Initial contact angle of G1~G4 ................................ ................................ .......................... 70 3 37 Change of contact angle with increasing of abrasion cycles for white green mixed paint ................................ ................................ ................................ ................................ .... 70 3 38 Higher pigment volume percent yields higher initial contact angle red paint system ...... 73 3 39 Contact angle fluctuates with abrasion cycles increase red paint/ 600C sand paper ........ 73 3 40 Contact angle changing trend of red paint/ 600C sand paper ................................ ........... 74 3 41 Weight change in percentage against abrasion cycles increase red paint/ 600C sand paper ................................ ................................ ................................ ................................ ... 74 3 42 List of wear index, weight loss (%), and slope of regression line (CDR) for by varying the volume percent of pigments adding red paint/ 600C sand paper ................. 75 3 43 Appearances of R1 to R4 ................................ ................................ ................................ ... 75 3 44 Initial contact angle of R1 R4 ................................ ................................ ............................ 76 3 45 Change of contact angle with increasing of abrasion cycles for white red mixed paint ... 76 3 46 Correlation of initial contact angle and volume percent of pa rticles ................................ 78 3 47 Different ratio of particle and polymer turns out different structure ................................ 78 4 1 Polymeriza tion behavior of aqueous silica. ................................ ................................ ....... 82

PAGE 13

13 4 2 C ontact angle image for sample with 69V% of particle ................................ .................... 86 4 3 Contact angle change with wiping cycles increase for samples with different silica particles volume percent ................................ ................................ ................................ .... 87 4 4 Transmittance vs. wavelength with black glass, weak surface coating, and durable surface coating ................................ ................................ ................................ ................... 88 4 5 Camera photo for weak (87V%) and durable (69%) coating ................................ ............ 89 5 1 Common formula of silane coupling agents ................................ ................................ ...... 91 5 2 Dissociation energy of X Side leaving group, from Gelest Inc. [41]. ............................... 91 5 3 Schematic of a silicon oxide particle bonded to glass surface via oligomer chain. ........... 92 5 4 Schematic of thiol disulfide bond formation between silica particle and glass slide ........ 92 5 5 Formation and reactions of sulfenic acid [43] ................................ ................................ ... 93 5 6 D reaction time 24hrs ........... 96 5 7 R educed oxidation time enhanced t he durability of coating reaction time 30 mins .......... 96 5 8 Contact angle change against abrasion cycles ................................ ................................ ... 97

PAGE 14

14 LIST OF ABBREVIATIONS CB state Cassie Baxter state CDR C oating de pletion rate DMF Dimethylformamide EtAc Ethyl acetate MPTMS (3 Mercaptopropyl) trimethoxysilane PMMA Polymethyl methacrylate PVDF Polyviny lidene difluoride SH Superhydrophobic SBS Standard binder solution UV Ultraviolet WCA Water contact angle

PAGE 15

15 Ab stract of Disse rtation Presented t o the Graduate School of the University of Florida i n Partial Fulfillment o f the Requirements for the Degree of Doctor of Philosophy STRATEGIES FOR ENHANCING THE MECHANICAL DURABILITY OF TRANSPARENT SUPERHYDROPHOBIC COATI NG AND DEVELOPMENT OF COLOR AND DURABLE SUPERHYDROPHOBIC PAINT By Yung Chieh Hung August 2016 Chair: Wolfgang Sigmund Major: Mat erials Science and Engineering Superhydrophobic surfaces feature repellency of liquids and enhance existing or enable nove l technologies such as self cleaning, have anti fouling behavior, and ice phobicity. Superhydrophobicity is quantitatively described by surface science theories such as the Cassie Baxter model. From this model it is obvious that changes in the surface chem istry due to oxidation or surface topography due to abrasion or aging causes the coating to lose its superhydrophobic property. This lack of durability in products currently limits the commercial breakthrough of this technology. This dissertation addresse s four major objectives. 1) Development of a quantitative durability test that could be standardized. 2) Develop a composite paint for durability. 3) Understand the structure of durable superhydrophobic coatings. 4) Apply this knowledge to build the ultim ate coating which is superhydrophobic, durable and transparent. Such a coating could be applied to any material or device without changing its looks and is most desired by a large number of companies throughout the world. This dissertation addresses the a bove mentioned challenges first by developing and then testing and applying a new wear resistance measurement approach for superhydrophobic

PAGE 16

16 coatings, which could be used for standardization in this field. It is built on existing ASTM standards (ASTM D4060 14) with modification s for superhydrophobic surfaces. Moreover, the advances achieved by using this standard for characterizing samples allowed the development of novel superhydrophobic coatings that are durable. The concept that was applied is based on capillary and funicular structures in mostly dense composite materials consisting of hydrophobic polymers with hydrophobic ceramic particles. The volumetric thick thermoplastic component of the paint layer gives it the mechanical strength to achieve superh ydrophobicity through 1000 abrasion cycles by metallurg ical sand paper. The scalability was addressed by formulating this coating as a paint. This allows for application in large areas, and the possibility to add color s beyond white, which in this work are black, blue, green and red. The concept allows to fabricate any other type of color ed paint as long as the pigments can be hydrophobized or are themselves already hydrophobic By varying the particle volume percent, threshold to achieve superhydropho bicity could be demonstrated in this way. This research states the threshold to attain superhydrophobicity is around 60V% 70V% of particle no matter what pigments were selected. This value is also the transition point from capillary structure to funicular structure. The application of this breakthrough to transparent SH coatings is of course more challenging. In order to achieve durable and transparent SH coating, novel approaches are reported in this dissertation. Moving from an organic inorganic paint s ystem to a ceramic ceramic system allows to reduce scattering induced by the variation in refractive indices of the components. A silica sol gel is used to enhance mechanical and che mical bonding of nanoparticles. Threshold to achieve superhydr ophobicity is also located in 60V% to 70V% and fulfill our expectation. Moreover, a second novel concept using particle agglomeration and bonding to enhance transparent superhydrophobic material is introduced. Monodisperse silica

PAGE 17

17 nanoparticles were treate d with a variety of silane coupling agents. By doing so, the silica nanoparticles became functionalized with reactive groups that allowed bonding under specific conditions. The introduction of directly chemically bonding particles further enhanced the dura bility. However, a lot more needs to be done since the scattering limits of the materials in composites or just the surface features alone make it challenging to provide the proper surface architecture and chemistry while being mechanically robust to withs tand abuse. In summary this work advances the field of superhydrophobic coatings, applies the theories and standards for characterization, and demonstrates them in examples of novel durable ceramic polymer and transparent ceramic ceramic composite coatings

PAGE 18

18 CHAPTER 1 SUPERHYDROPHOBIC AND HYDROPHOBIC MATERIALS Introduction Superhydrophobicity was discovered from natural phenomenon, the most famous of these being the lotus effect [1] [6] Superhydrophobic (SH) materials ar e versatile and possess fascinating properties such as: 1. Self cleaning property [7] [13] This is one of the most important phenomena of superhydrophobic surfaces. When a water droplet rolls off the surface, it picks up dirt and keeps the surface clean. Superhydrophobic coatings could keep surfaces clean via flu shing by natural raining, reducing consumption of water. Namely, SH material can be considered a green material. 2. Anti biofouling surfaces : With lower surface energy, SH material can reduce the displeasing adherence of bacterial and bio films. SH materia ls have the potential to replace toxic coatings used in marine applications, such as tributyltin (TBT) and triphenyltin (TPT) [14] 3. Drag force reduction : In the cassie baxter state, a thin layer of air is trapped between the SH surface and wate r. So partial interaction between solid and liquid vanishes, and this reduction can be as high as 50% [15] With water repellent coatings on the surface, watercraft could be more energy efficient. Given these advantages, SH materials have attracted researcher s attention in the last decade. Theoretically, a super hydrophobic surface is defined as a s urface where the water contact angle (WCA) is greater than 150 and the roll off, or sliding angle is less than 10 tilt from horizontal. Literature has demonstrated that the basic theory of superhydrophobicity can be divided in to two main sections [3], [5], [6], [16], [17] Surface roughness, or morphology, and th e lotus effect are mainly built on this concept. Tiny protrusions on the lotus or taro leaves provide a high roughness factor and result in contact angles being >150 and self cleaning properties. Second ly not only does roughness play an essential role, so d oes surface chemistry. Without proper chemistry, a surfac e loses self cleaning or other S H properties, even though it has high contact and sliding angles. In this situation, also called the Wenzel state, the surface loses its superhydrophobic charact eristics. Therefore, surface chemistry determines whether the

PAGE 19

19 surface can reduce the attraction between water and surface, and low surface energy chemicals or materials must be selected to achieve superhydrophobicity. Wetting Theory Surface T ension Surfa ce tension is caused by an imbalance of attractive forces at the surface, where atoms, molecules or ions are surrounded by a reduced number of similar materials or have larger distances to their nearest neighbors. For liquids, this results in the molecule s on the surface being energetically unstable. Therefore, the surface creates a force to try to minimize the number of systems or free surface energy in solid materials. These units can be interpreted either as tension force per unit length of a line (e.g. N/m) or as energy per unit surface area (J/m 2 ) at the surface. Wetting Equilibria In terms of contact between two substances, there are multiple types of we tting, no matter those substances are liquid or solid. Three types of wetting are reported by Osterhuf, 1930, which are: (1) spreading wetting, (2) adhesion wetting, and (3) immersional wetting. Fig ure 1 1 Spreading wetting

PAGE 20

20 In F ig ure 1 1, the liquid air interface moving from point C to point B causes a change in the surface energy of the whole system. For spreading to occur spontaneously, the energy change should be negative. The energy change is because the system loses solid air interface and gains solid liquid, liquid air interface by area a. Because (1 1) The term the spreading coefficient, is the driving force and determines whether the spreading process occurs spontaneously or not. If liquid will spread ov er the whole substrate. If liquid will stop spreading at a certain point, which is where contact angle comes in. Contact Angle Figure 1 2 Contact angle While substrate is solid, liquid wets the surface and forms a spherical cap with stat ic energy from three phases

PAGE 21

21 (Figure 1 L/S interface, an area increase in the L/ interface. Hence, the energy change could be calculated as (1 2) if this equation can be rewritten as (1 3) (1 4) c the liquid tends to spread on the surface. It is usually referred to as hydrophilic or o leophilic surface in terms of aqueous or oily liquid, respectively. If the value of the contact angle is 90 c 18 0 the wetting area tends to shrink and forms a spherical droplet. If the CA is over 150 the surface is referred to as superhydrophobic C lassical Models for Contact Angles o n Rough S urfaces Wenzel State The Wenzel model considers a homogeneous solid liquid interface where the solid ideally fla t surfaces that are atomically smooth and chemically homogeneous. In reality, very few solids are atomically smooth. Therefore, the roughness should be taken into consideration. In the Wenzel state, where the roughness is compl etely filled with liquid, t he water contact angle in Wenzel state ( ) can be described by : (1 5)

PAGE 22

22 Where R f is called the roughness factor which is defined as: (1 6) Since R f is always positive when the CA is less than 90 0 the roughness factors cause smaller contact angles; however, if the CA is larger than 90 0 the R f causes a larger contact angle. In other words, the roughness factor makes hydrophilic surfaces more hydroph ilic and hydrophobic surfaces more hydrophobic. Heterogeneous Solid Liquid Interface: Cassie Baxter Model Furthermore, the Wenzel regime is usually recognized as homogeneous wetting, since the liquid completely penetrate s the grooves. Yet, under superhyd rophic circumstances, vapor pockets may become trapped underneath the liquid yielding a composite surface ( Figure 1 3 c). This heterogeneous wetting is illustrated by Cassie Baxter theory, where the contact angle can be predicted by equation: (1 7) Where equation, and f s and f v are the contact area fraction of the solid and vapor. Because f s + f v =1 and = 180 (because liquid droplet in the air is a perfect sphere), this equation could be modified to: (1 8) F rom Eq.1 7 and Eq.1 8 the lesser contact area of liquid to solid substrate leads to a higher contact angle in the Cassie Baxter state (usually suitable when water contact angle is higher than 150). With this equation, could be calculated once is measured T he calculation value listed in this dissertation was based on this equation

PAGE 23

23 (A) (B) (C) Cassi Figure 1 3 Wetting behavior of a liquid droplet on solid surface and their mathematical models. A) A liquid droplet on an ideally f B) Liquid droplet on a rough surface, Wenzel model, C) Vapor pockets are trapped between the grooves and the liquid droplet, Cassie Baxter model. Contact Angle Hysteresis While the preceding section is for the static contact angle model, there is another met hod to evaluate the superhydrophobicity. The contact angle hysteresis is also an essential characteristic of a solid liquid interface that is affected by the roughness and chemical inhomogeneity of a surface. Superhydrophobic coatings should not only have high contact angle but also low contact angle hysteresis and sliding angle. Contact angl hys is defined by Eq.

PAGE 24

24 (1 9) and are the advancing angle and the receding angle, respectively. The advancing angle is the maximum value of contact angle before the liquid solid contact line begins to advance; contrarily, the receding angle is the minimum value of contact angle before retreat. Hence, the static contact angle is always in this range which is Advancing and receding angle are usually measured by sessile drop measurements, where water is pumped into or withdr awn from a stat ic droplet (Figure 1 4). Figure 1 4 Contact angle hysteresis. A ) Advancing angle ( ) is the maximum contact angle of a droplet before its contact line (liquid solid interface) starts adv ancing. B ) Receding angle( ) is the minimum contact angle of a droplet before its contact line starts to receding. Transition between Cassie Baxter a nd Wenzel State According to Equations 1 5 and 1 7 two conta ct angles are defined differently for a Baxter state is a metastable state that only occurs in superhydrophobic regime. Several reports have mentioned solid/liquid contact mode shifted from Cassie Baxter state to Wenzel state by external physical pressing [18], [19] Jose et al [20] demonstrated the threshold value of Cassi e Baxter state to Wenzel s tate could be written as (1 10)

PAGE 25

25 Where f s is the contact area fraction of solid and r is the rou ghness factor. Interestingly, f s is smaller than 1 and r is bigger than 1. These tu rn the right side of equation 1 8 to negative and means solid is lower than the value given by eq. (1 8), trapped air pockets are not stable, and the Wenzel mode will dominate. To meet the criteria for the Cassie Baxter state to exist, a solid substrate should either be hydrophobic enough or the roughness factor must be high. Contact Angle Measurement Contact angle measurement is carried out by acquiring images of resting drops on the surface through a specific appara tus, the goniometer. A goniometer could help us to measure the static water contact angle and contact angl e hysteresis, as shown in Figure 1 5 below. Figure 1 5 Image of contact angle measurement. A ) Static water contact angle measurement B ) contact a ngle hysteresis measurement (1 11) However, a recognized protocol of measuring has not been established. Although using the same system and equipment, the results may change if the measurements are performed with slight va riation s Hence, some factors should be taken into consideration:

PAGE 26

26 1. Drop size : The drop size should be large enough compared to the surface features [21] If the drop size is too large, the drop shape may be distorted by the gravity. Drops that are too small are difficult to be placed on the test surface, especially on a superhydrophobic sample. Generally, the standard i s 10l, and using the same size of drops throughout the whole measurement is essential. 2. Drop placement : Most of the tests for superhydrophobicity are located in the meta stable, Cassie Baxter state, regime where the drops are triggered to change to a more stable state, the Wenzel state, by external forces. The solution minimizes the kinetic energy of drops before taking images. 3. Image quality : Acquiring a clear image is probably the most crucial part of conducting the measurement. The backgroun d should be as clear as possible, especially on the bottom portion. This is challenging when dealing with superhydrophobic surfaces since the contact angle is high, and the drops have limited contact area on the surface. Sometimes, an extra light source i s necessary to optimize the image quality. All these factors are essential and should be taken into account during contact angle measurements. The key is to perform a measurement in the same conditions, and report the conditions and parameter s clearly. Tr aditional Superhydrophobic Surface Fabrication Like previously mentioned, surface chemistry and surface roughness are two key factors needed for achieving superhydrophobicity. Briefly speaking, mo u lding and photolithography are typical approaches to build surface features. Making Hairy Surface v ia Moulding Techniques: Hs u e t al [22] casted hairy structures made of micro size polypropylene using track etched polycarbonate membranes. Figure 1 6 shows the pore size of a comm ercial poly carbonated membr ane and the diameter was around 3 m. They attached a polycarbonate membrane to a polypropylene substrate, and applied heat and pressure. Once the temperature surpassed the Tg of polypropylene, the PP substrate turned to plastic, which filled in the pores. Afterwards, the membrane was peeled off and the hairy polypropylene structure was obtained; the process flow is shown in Figure 1 7

PAGE 27

27 Figure 1 6 Commercial polycarbonate membrane with pore size 3m ( Photo c ourtesy of Shu hau and Dr. Wolfgan g Sigmund) Figure 1 7 Fabrication of superhydrophobic from polypropylene a ) Process flow of PP hairy structure superhydrophobic surface ) SEM image of hairy structure. c ) Con tact angle of PP flat surface.d ) Contact angle of PP hairy structure surface ( Photo c ourtesy of Shu hau and Dr. Wolfgang Sigmund) Casting Fine Surface Structure v ia Photolithography In the review paper written by P. Roach et al [23] they organized 9 reports which fabricated fine structures via photolithography. Fine structure is appli cable to demonstrate the

PAGE 28

28 superhydrophobic theory and discuss how roughness affect s contact angle. With fine and shape unitary structure, roughness could be calculated to prove Cassie Baxter state to Wenzel state transition. However, photolithography is a c ostly approach and not scalable. Current Limitations o f Superhydrophobic Materials Mechanical Durability To conclude, plenty of papers have been posted which contain novel, creative approaches to fabricate superhydrophobic coatings and materials. Nev ertheless, until recently, none of these were turned into a commercial product Simpson et al [24] reported possible reasons which are: 1. Cost issues: Because micro or even nano features are necessary for a superhydrophobic coating, most o f the early research used photolithographic processes to fabricate the fine surface structure, which is costly and has limited applicability to greater area. 2. Nano structure stability and coating durability: Surface features are essential for superhydro phobic coatings. However, these structures are vulnerable against shear force, and once the surface features are removed or destroyed, the surface turns hydrophobic only. Figure 1 8 shows a hairy structure of a polypropylene surface that was destroyed by a finger touch and lost superhydrophobicity. Micro structures on a silicon wafer were damaged by sand particles as shown in the SEM image in Figure 1 9. [19] Figure 1 8 Superhydrophobic hairy polypropylene surface a) Before finger touching. b) Surface wa s des troyed by the touch of a finger. Reprinted with permission from Hsu, S. H.; Sigmund, W. M. Artificial Hairy Surfaces with a Nearly Perfect Hydrophobic Response. Langmuir 2010, 26, 1504 1506.23

PAGE 29

29 Optical Property Apart from mechanical wear resistance superhydrophobic coating is usually blurry because of light scattering caused by surface roughness. T ransparent superhydrophobic coatings could for example be applied on solar cell panels to keep them clean and at their highest efficiency [25] [30] Cars would not need washing as long as it rains sometimes and amount of bacteria, viruses and dust could be lowered overall in operating rooms and hospitals by such coatings. Several reports exist that demonstrated transparent superhydrophobic coatings usi ng nanoparticles that are below the Fraunhofer and Mie scattering for light. However, all these coatings suffer from lack of durability. This is due to the oxidation of the materials and the low thickness of the coating For the transmittance part, a lthoug h some previous work has fabricated transparent and superhydrophobic coatings via lithographic procedures to create the nano scale features on the substrate, this approach expresses distinct limitations for large scale application. More recently, plentiful reports claim that superhydrophobic and transparent coating has been achieved and developed. Nevertheless, after scrutiny, the transmittance is not high enough (with most <90%) to be considered transparent Current Measurements for Mechanical Durability o f Superhydrophobic Surface Although some reports announced the development of durable superhydrophobic materials, techniques used to evaluate properties are inconsistent, and the standards regulating the conditions and information needed to be reported ar e absent. A brief summary of the techniques are shown in Table 1 1 Although researche r s provided many ways to test the durability of superhydrophobic material N one of them is a quantitative way to depict the resistance of superhydrophobic material. Therefore, a new stand to describe the wear resistance of SH material is necessary.

PAGE 30

30 Table 1 1 Current methods to measure wear resistance of SH material Table 1 2. Current methods to characterize wear resistance of SH material Chapter Summary Superhy drophobic material possesses self cleaning property which interests researchers the most With SH coating, dust could be flushed away by rain and adhesion of dust could be reduced due to low surface energy of SH surface To achieve superhy drophobicity, trapped air pockets between surface feature and water droplet should be stable. So water droplet can move freely on the SH surface and Cassie Baxter equation could be used to describe the water contact angle behavior. Howe ver, CB state is a metastable stage so that if exterior force comes in, wetting behavior of water droplet would be driven to Wenzel state which is the stable state. Energy barrier of CB Wenzel transition was also introduced and this equation tells that in order to stabilize CB state, surface energy should as small as possible and surface roughness factor should be as high as possible. With this perspective, SH material s ha ve been fabricated in plenty of approaches such as moulding or photolithography. Neve rtheless, current adversit y for Methods of Mechanical Wear 1. Sample rubbe d against clothes [31] [33] 2. Sample rubbed against sand paper [32], [34], [35] 3. Sample rubbed against synthetic leather under a certain load [36] 4. Sample Abraded by cotton swab [37] 5. Sample Abraded by steel woo l 6. Ball on disk test [38] 7. Sand abrasion tes t [39] 8. Adhesive tape [40] 9. High speed current scouring or water jet test [41] Characterization of mechanical wear 1. Change in contact angle hysteresis [32] 2. Water shedding angle [36] 3. Roll off angle [31] 4. Coefficient of friction [38] 5. Static contact angle [33]

PAGE 31

31 application of SH material is durability. Several papers claimed they made durable SH surface but the durability test is not standardize d and controversial.

PAGE 32

32 CHAPTER 2 FABRICATION OF DURABLE AND SUPERHYDROPHOBIC PAINT WITH COMMERCIAL FLUORO POLYMER Introduction Several superhydrophobic surfaces are observed in nature, but their structures are also vulnerable to mechanical shear forces. Why, then, could they always possess superhydrophobic properties? The answer is rege neration. Artificial material is not able to regenerate surface regeneration. More specifically, a coating which can regenerate the rough surface and still posse ss the superhydrophobicity after wear is our core objective. Once the top layer of particles or nanofibers is removed, a second layer reveals the surface is still rough enough to show superhydrophobicity until whole coating is wiped out. One paint manufact uring company also [24] In C hapter 2 the Lumiflon 4400 was chosen as the binder to form a polymer matrix, and the pigment was fumed silica. Silica carries the most suffi cient hydroxyl group for the surface comparing to other ceramic particles, and a hydroxyl group is crucial for further silane bonding, such as perfluoro trichlorosilane or aliphatic alkyl silane. The density of the hydroxyl group strongly influences the ul t imate silane density from which the hydrophobicity of particles come. Fluorinated silica particles were mixed with Lumiflon 4400 fluoropolymer in differing volume percentages. Threshold value to achieve superhydrophobicity is reported. Wettability change against wear, wear resistance and coating depletion rate (CDR) are also reported. St andardize Wear Resistance Test f or Superhydrophobic Coating/ Material Although plenty of papers have announced durable superhydrophobic coating have been demonstrated alre ady [36], [42] [50] The tes ting methods are not unified and standar dized, which are listed in the T able 1 1. Therefore, ASTM D4060 14 [51] and ISO 7784 2 are

PAGE 33

33 referenced as guidelines to quantify the durability of superhydrophobic materials. These two standards demonstrate a sound process to evaluate the wear resistance of test specimen. The terminologies to express abrasion resistance listed in ASTM D4060 14 are: Wear in dex, n 1000 times the loss in weight in milligrams per cycle Weight loss, n the loss in weight in milligrams, determined at a specified number of cycles. Wear cycles per mil n the number of cycles of abrasion required to wear a film through to the substra te per mil (0.001 in.) of film thickness. The experimental process is summarized here: An organic based coating with a certain thickness is attached to a rigid panel and abraded by rotary rubbing action under controlled loading and environment. Abrasion resistance is calculated as loss in weight after a specified number of abrasion cycles, as loss in weight per cycle, or as number of cycles required to remove a unit amount of coating thickness. ASTM D4060 records some conditions need ed to be presented in the report, which are: 1. Temperature and humidity conditions during and at the time of testing 2. Thickness of coating when wear cycles are specified 3. Type of abrasive wheels used 4. Load applied to the abrasive wheels 5. Number of wear cycles recorded for each test specimen 6. Wear index, wear loss, or wear cycles per mile for each test specimen Given the required properties of SH surfaces, which are 1) Static contact angle is over 150 and 2) Sliding or roll off angle is smaller tha n 10 , two measurements are proposed to classify the wear resistance of superhydrophobic material. Measurement of Water Contact Angle Change a gainst Abrasion Cycles A wear resistance test should include the contact angle and sliding angle change compared information should be reported as well. For example, silicon carbide sand papers with different

PAGE 34

34 grits result in different friction behavior. Other conditions such as temperature, co ating thickness, loading, and type of abrasive are also need ed to be reported. With this information, researchers are able to understand the critical point where coatings lose superhydrophobicity. Measurement of Weight Loss a gainst Abrasion Cycles Weight loss could be used to calculate the wear index and wear loss. This value could help researche r s to evaluate how fast the coating degrades under abrasion. The weight of a sample is measured every 200 cycles with accuracy of 0.1 mg. After wards the data po ints could be fit in linear regression and the slope can be obtained, which could be defined as coating depletion rate (CDR). Other conditions, such as temperature, coating thickness, loading, and type of abrasive, need to be reported. Novel Design Perspe ctive o f Durable Superhydrophobic Coating F ig ure 2 1 illustrates the reason why traditional design of SH fabrication is fragile. After abrasion, the top of the structure is damaged, and two situations would occur. First, if the surface feature is made of intrinsic hydrophobic material such as polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), polystyrene (PS) etc loss of surface roughness causes contact angle to decreas e sharply and triggers CB state Wenzel state transition. So, superhydrop hobicity vanishes. If surface features are intrinsic hydrophilic they can still be hydrophobized by perfluoro silane or aliphatic silane. However, once the surface is damaged, the new surface will become hydrophilic. Hence, although the surface features ar e strong, minor surface damage influences the wettability. In this dissertation, a new perspective will be brought in to solve this disadv antage. Figure 2 1 B illustrates how this new design works; the white circles are hydrophobized metal oxide particles or nanofibers, and the yellow substrate represents the polymer matrix. After drying, the whole coating can be considered a particle polymer composite material with thickness L and weight W. After abrasion, the top layer of the coating is

PAGE 35

35 removed, and middl e layer particles ascend to the surface, with retention of a random rough surface. Therefore, wettability could remain unchanged as long as the coating is not totally wiped off. After certain abrasion cycles, coating thickness drops to L' and weight change s to W'. By depletion rate (CDR). Researchers can use this quantified data to understand the durability of coating and evaluate the strength of coating. Figure 2 1 Difference of traditional design and new design. A) Traditional one layer design after abrasion B ) Multilayer design after abrasion Stacking o f Granular Material Gabrieli et al [52] elucidated the behavior of partial ly water saturated solid granules and divided them into five stages, shown in Figure 2 2. At the solid volume percent 100%, particles stack together without any water content. Packing density of particles are in the range of 56%~ 64%, which is also the empirical re sult of random closed packing. As the increase of liquid

PAGE 36

36 portion, final structure transfers from dry to saturated stage. In pendular stage, particle grain is connected by little polymer and this polymer forms so called capillary bridge or pendular ring. In funicular s tate, pendular rings collapse and shared by more solid grains instead of connecting only between two solid grains In capillary state, polymer domain is major rather than air domain. Therefore, Strength of final structure goes up with lower par ticle percentage but wall roughness of final structure decrease s. To achieve durable superhydrophobic coating, both wettability and durability should be considered in the same time However, final dried material with higher particle portion yields higher w all roughness but weaker structure. A criterion that provides enough wall roughness to achieve superhydrophobicity and possess decent strength, should be demonstrated. Figure 2 2 Schematic of final dried material with different particle polymer ratio Particles a nd Polymer Selection Again, both chemistry and roughness determine the final wetting behavior of the surface. Submicron nanoparticles or nano rods could be used as a surface roughness contributor after being hydrophobized by our new design. Polymer binder selection is also significant here and is confined to intrinsic hydrophobic material category. Lumiflon 4400 is a water borne fluoro polymer and possess 10 0 initial contact angle. Figure 2 2 shows the chemical structure of

PAGE 37

37 Lumiflon 4400, w hich consists of tri fluoro units and hydrophilic functional groups. With sufficient fluoro units, Lumiflon 4400 is an intrinsically hydrophobic polymer and fulfills our demand. Figure 2 3 Chemical structure of Lumiflon 4400 from Asahi Fabrication of Water Borne Superhydrophobic and Durable Coating w ith Commercial Fluoro Polymer Materials a nd Experimental Process Fabrication of superhydrophobic white pigments Silica particles were purchased from Evonik Industries with the product name Aerosil Ox 50. T he specific surface area is 35 65 m 2 / g. The processing starts with silica particles being dehydrated in the oven at 120 C and then dispersed in chloroform. Subsequently, heptadecafluoro 1, 1, 2, 2, tetrahydrodecyltrichlorosil ane, which is from Gelest In c., was added to the silica chloroform dispersion with the ratio 1 ml : 1g silica and treated for 1 hour. Afterward, centrifuging the dispersion and decanting the chloroform follows. Drying of particles is done at 120C on a heating plate for 5 hours. The fl uorinated silica particles are obtained in this way. Preparation of coating samples with different V% These silica particles were combined in different proportions with Lumiflon FE 4400, a commercial water based fluoropolymer resin emulsion used to produ ce coatings with high gloss and increased weatherability. Based on volume percent calculations, solutions ratios of

PAGE 38

38 fluorinated silica to Lumiflon of 55V%, 60V%, 65V%, and 75 V% were mixed. Additionally, ethanol was added as a solvent to help disperse the p articles and aid in faster drying. These solutions were mixed using a vortex mixture as well as with magnetic stirring bars for at least 6 hours. Sample preparation Soda were cleaned by isopropanol and left to dry in air for a minimum of 10 hours. Method of measurement Contact angle measurements were taken from high resolution photos of 30 L DI water droplets by using Image J. Durability testing was performed using a Tab er 5700 li near abrader and 1200C grit silicon carbide me tallurgical paper, manufactured by ALLIED high tech products Inc. The loading pressure was 0.98N and the wear index was also calculated from weight loss after every 200 cycles, up to 1000 cycles. (Definition of wear index is from ASTM D4060 14.) Weight loss measurements were obtained by a TR104 Denver Instrument scale with an accuracy of 0.1mg. Results a nd Discussion Initial Contact Angle of White Coating w ith Different V % Pigments Adding In Figure 2 4 ratio of fluorinated fumed silica was adjusted fro m 55V% to 75 V%. In our expectation, higher volume percent of pigments in the whole coating should cause higher contact angle and better wettability. From equation 1 10, higher roughness should stabilize water droplet in Cassie baxter state. Therefore, the contact angle increasing trend could be understood. Furthermore Figure 2 4 illustrates how polymer distributed in particles polymer composite. Volume percent of polymer decreases from left to right and expresses different distribution

PAGE 39

39 status. Because of s urface tension and capillary force, polymer tends to adhere on the surface of particles and pores would be created in the polymer matrix. This is also called funicular sta ge. With increasing in particle ratio, polymer bridge forms and chains each particles together. Therefore, higher V% of adding pigments lead s to polymer distribution stage shifting from saturated to pendular and enhances surface roughness factor. Figure 2 4. Higher volume percent of fluorinated silica adding turns out higher initial co ntact angle Figure 2 5. Scheme of polymer distribution status with different volume percent in particle binder composite

PAGE 40

40 Abrasion Test w ith 1200P Sandpaper a s Abrader Lumiflon White Paint System Abrasion test was operated by Taber linear abraser and lo ading was 0.98N and contact angle and weight were measured every 200 cycles. Contact angle change and weight change are listed in the Figure 2 5 and Figure 2 6. In Figure 2 5, 75V% sample, which possesses the weakest structure, was wiped out before 400 cyc les so only two points were shown. 65V% sample was also demolished before 600cycles. Trade off occurs between wear resistance and wettability. 60V% sample survived a fter 1000 time s abrasion by 1200C sand paper. Contact angle was around 151 2 after 1000 t ime abrasion. However, contact angle of 55V% sample was dropping gradually with abrasion cycles increasing. The reason is that structure of 55V% is stronger than 60V% so that polymer matrix of 55V% was not damaged by 1200C sand paper which means only particles on the top layer w ere removed. In doing this, a new layer of particles ed intrinsic contact angle of Lumiflon resin eventually which is around 120 Figu re 2 6. Water contact angle change against abrasion cycles Lumiflon white paint system ( : 75 V%, : 65 V%, : )

PAGE 41

41 CDR of 75V% sample was the highest and reached 100% loss before 400 cycles and 65V% loss 100% before 600 cycles. Interestingly, 60V% and 55V% lost around 16% and it may not be wiped out until 10,000 cycles. Figure 2 7. Weight change against abrasion cycles Lumiflon white paint system ( : 75V%, : 65V%, Combine the result in Figure 2 6 and Figure 2 7 particle volume percent 55V% to 60V% is preferable to make durable superhydrophobic coating. Su mmary In Chapter 2, new perspective of superhydrophobic material was introduced. Unlike the traditional one layered surface feature, new design used multi layered structure to overcome durability issue in old design. The idea is that o nce top layer of coat ing is re moved, new layer of particle reveals itself and provide s roughness so that coating can possess superhydrophobic ity until whole coating is destroyed. Moreover, durable superhydrophobic white paint was successfully made of fluorinated silica par ticles and commercial fluoropolymer. By varying the

PAGE 42

42 volume percent of pigment 55V% to 60V% was found to be the critical range in which coating was still in superhy drophic regime after 1000 times of abrasion with a loading of 0.98N. This is the first report with quantitative wear resistance of superhydrophobic material. Also, f irst superhydrophobic coating that could be worn 1000 times by sand paper was illustrated and this result has been patented.

PAGE 43

43 CHAPTER 3 FABRICATION OF DURABLE AND SUP ERHYDROPHOBIC COLOR PAINTS Introduction In Chapter 2, a durable superhydrophobic white coating was made successfully, and changing the traditional superhydrophobic one layer surface feature to a multilayer structure was demonstrated. In Chapter 3 we fol low this core perspective and reduce dependence on commercial products. PVDF PMMA mixed polymer was chosen to be the main components of the polymer matrix. In the first part, white paints were made with different volume percent of pigment; wettability, con tact angle change with abrasion and coating depletion rate (CDR) were reported. To improve the applicability of these superhydrophobic coatings, black, blue, red, and green superhydrophobic coatings were created as well. Most natural color mattes are meta l oxide compounds; metal oxides have abundant hydroxyl groups on the surface where the surface modifier aims to bond. For example, ultramarine is a common blue matte, iron oxide can be used to make red and black paints, and chromium oxide is for green pain t fabrication. After fluorination, these color mattes can be used to fabricate superhydrophobic color paint. Although only 5 different colors of paints were reported in this dissertation, other colored superhydrophobic paints could be achieved by this appr oach as well. In Chapter 2, white superhydrophobic paint was created with different volume percent of pigment. The results show that a higher volume percent of pigment yields higher roughness because the polymer matrix distribution shifts. In Chapter 3 V% is still the parameter, and thresholds of V% to achieve superhydrophobicity (CA> 150 ) were all found in the range of 60V% to 70V% for different colors of paint. This point is the transition point from capillary state to funicular state and also the highe st possible packing density of random close packing. This range could be used a general principle to fabricate durable and superhydrophobic volumetric coatings

PAGE 44

44 Superhydro phobic White Paint Fabrication a nd Characterization Materials a nd Experimental Proce ss Fabrication of superhydrophobic white pigments Aerosil Ox 50 Silica particles were purchased from Evonik Industries; the specif ic surface area is 35 65 m 2 /g. P rocessing of these particles was achieved by dehydrating the silica particles in the oven at 1 20C and dispersing them in chloroform. Subsequently, heptadecafluoro 1, 1, 2, 2, tetrahydrodecyltrichlorosilcane, from Gelest Inc., was added to the silica chloroform dis persion with the ratio 1ml : 1g silica and treated for 1h. The dispersion was then cen trifuged; decanting of the chloroform followed dispersion. The particles were dried at 120C on a heating plate for 5hs, yielding the desired fluorinated silica particles. Binder blending The PVDF source was Kynar Hsv 900 with a molecular weight of 900, 000 1,300,000 g/mol. The PMMA used, from Polyscience Inc., was a blend of: 3.96g DMF, 0.21g PVDF, 0.8g acetone, 0.04g PMMA, 1g triethyl phosphate, and 100 l perfluoro compound F 75C (purchased from ACROS). A vortex mixer was then used to homogenize the l iquid part of paint. This paragraphs. Preparation of coating samples with different V% After blending the binder, fluorinated silica particles were added at dif ferent volume percent: 65.22% (with 0.6g fluorinated silica particles added), 61.08% (with 0.5g fluorinated silica particles added), 55.85% (with 0.4g fluorinated silica particles added), 48.57% (with 0.2g fluorinated silica particles added) and 38.46% (w ith 0.2g fluorinated silica particles added). lime glass slides were coated and spun at 100 rpm by a spin coater. The slides were dried in air for at least 10 hours.

PAGE 45

45 Method used for measurement C ontact an gle measurements were taken from high resolution photos of 15 L DI water droplets using Image J. Durability testing was performed using a Taber 5700 linear abrader and 1200P grit silicon carbide metallurgical paper, manufactured by ALLIED high tech produc ts Inc. The loading pressure was 0.98N, calculated out to be about 50 kPa, and the wear index was also calculated from weight loss after every 200 cycles, up to 1000 cycles. (Definition of wear index is from ASTM D4060 14.) Weight loss measurements were obtained by a TR104 Denver Instrument scale with an accuracy of 0.1mg Results a nd Discussion Initial Contact Angle Measurement Coatings with different pigment volume perce nt yield different initial WCA, and the results are shown in Figure 3 1. Obviously, c oating with a higher V% will have a higher initial WCA. According to the Cassie Baxter model, the contact angle depends on the fraction of contact material, which means that the rougher the surface is, the higher the WCA the material possesses. Interesting ly, there is a sharp increase in contact angle between paint with 55.85V% and paint with 61.08V%. Figure 3 1 H igher pigment V% yields higher initial contact angle white paint

PAGE 46

46 Contact Angle Change w ith Abrasion Test Figure 3 2 shows how contact angle d ecreases with increasing number of wiping cycles by various V% of pigments. In terms of our volumetric system design, once the top layer is removed, the second layer is revealed and still possesses superhydrophobicity until whole layer coating is wiped off Basically, five samples still have the trend of decreasing contact angles; however, 65.22V% and 61.08V% are still above 150 after 1000 abrasion cycles. Moreover, although the CA of the 55.85V% sample drops below 150 after 1000 abrasion cycles, it posse sses 147 contact angle, which is close to SH regime. This shows that lower V% samples, e.g. 38.46V% and 48.57% and 55.85%, degrade much slower than the paint with higher V% because the particles embedded in the binder matrix in the lower V% coating were i n a saturated status. The scheme of polymer distribution changes with the polymer vo lume percent as shown in Figure 3 4. In contrast, paint samples with higher V% suffered obvious contact angle decrease at beginning, but the trend gradually slowed. Figur e 3 2 Contact angle decrease s with abrasion cycles increase white paint ( : 65.22V%, : 61.08 V%, 55.85V%,

PAGE 47

47 Sample V% : 48.57 V% 55.85V% :61.08V% :65.22V% Slope of regression line of contact angle change 6. 3E 3 9.1 E 3 5.6 E 3 6.2 E 3 5.5 E 3 Figure 3 3 L ist of slope s of the regression line of decreasing WCA white paint system Figure 3 4 Scheme of polymer distribution status with different volume percent in particle binder composite Wear Index a nd C DR Calculation The definition of wear index is n 1000 times the loss in weight, in milligram per cycle, which is from ASTM D4060 14. Fig ure 3 5 shows weight los s of testing samples and Figure 3 6 lists the wear index corresponding to different V%. As the results show, 38.46V%, 48.57V% and 55.85V% have similar wear resistance and weight loss after 1000 abrasion cycles, around 5~6%. However, there is a jump between 61.08% and 55.85% because the binder distribution status changes from capillary stage to funi cular stage (shown in Figure 3 4 ), so that the weight loss of 61.08V% and 65.22% is larger than the lower V% coatings. In summary, the weight loss of the 5 samples after 1000 abr asion cycles is less than 15%. Interestingly, the random close packing density for slow settlement is 56%, which could be used to explain why we obtained two different coating depleting rates (CDR). Coating with V% lower than 56% show a thin film

PAGE 48

48 structure and possess a lower CDR. After the V% is over 56%, the polymer dis tribution b ecomes funicular or even pendular, making the structure less rigid. Figure 3 5 Weight loss with different volume percent after abrasion white paint ( : 65.22V%, : 61.08 V%, 55.85V%, Sample V% : 48.57 V% 55.85V% :61.08V% :65.22V% Wear Index (mg/cycle) 4.5x10 3 4.7x10 3 5.2x10 3 9.2x10 3 10.7x10 3 Percentage of weight change to initial weight after 1 000 cycles abrasion (%) 5.62 0.5% 5.87 0.5% 6.5 0.5% 11.5 0.5% 13.38 0.5% Slope of regression line (CDR) 4.91E 3 6.14 E 3 6.09 E 3 9.54 E 3 11.43 E 3 Figure 3 6 List of wear index, weight loss part per thousand, and slope of regression line for by varying the Volume percent of pigments adding SEM Characterization Figure 3 7 to Figure 3 10 show SEM images of the cross section of the paint s with 38.46V%, 55.85V%, 61.08V% and 65.22B% in sequence. The white circles indicate an enlarged

PAGE 49

49 area for the image i n higher magnification. In Figure 3 7, the final dried material forms a thin film like structure because th e polymer distribution is in capillary state (shown in Figure 2 2 ) and hydrophobized particles were surrounded by the p olymer domain. Therefor e, in this situation, lower roughness surface results in a lower initial contact angle ( only 140 ) bu t lower coating depletion rate (CDR) which means a more rigid structure. Figure 3 8 and Figure 3 9 show the cross section images of coating with 55.85V% and 61.08V%. Higher paritlce volume percent turns out a rougher surface and higher initial contact angle. Ultimately, the 65.22V% coating, which is shown in Figure 3 10, reveals a distinctl y different structure in Figure 3 7 Evident f rom the image, the structure has much rough er surface than image in Figure 3 7 The polymer distrib ution status is in the funicular state and formed flaky structure This the reason why depleting trend is faster than the coating with lower V%, the 65.22V% coating is still superhydrophobic after 1000 abrasion cycles. Figure 3 7 Cross section of coating with 38.46V% of particle and the polymer distribution is in capillary stage. (Photo c ourtesy of author)

PAGE 50

50 Figure 3 8. C ross section of coating with 55.85V % of particle (Photo c ourtesy of author) Figure 3 9 Cross section of coating with 61.08V% paint and the polymer distribution is in funicular stage (Photo c ourtesy of author) Figure 3 10. Cross section of coating w ith 65.22V% paint and particles are bonded by polymer bridge and show a flaky structure (Photo c ourtesy of author)

PAGE 51

51 Discussion a nd Understanding Based on the empirical statistic of random close packing, the possible packing density is in the range of 56% to 64% [53] [57] In order to understand the possible wall roughness of our final dried material, FCC (111) and simple cubic (100) were chosen to be the upp er limit and lower limit. FCC (111) is the close packed plane, whose packing density is 74%, in FCC struc ture and the calculated roughness factor is 1.9 ( shown in Figure 3 11 ) On the other hand, packing density of plane (100) in simple cubic structure is 52% and turns out roughness factor In the white paint system, d epend on the contact angle measurement ( Figure 3 1) and equation 1 5, 1 8, 1 10, wall roughness of final dried material with varied particle volume percent were calculated and shown in Figure 3 12. Roughness factors of sample 55.8V%, 61.1V%, 65.2V% are in the range of 1.78 1.9, which is our expected range. Figure 3 11. Calculated roughness factor ( ) of surfaces with packing density 74% and 52% Figure 3 12. Calculated solid fraction ( ) and roughness factor ( )

PAGE 52

52 Threshold to achieve superhydrophobicity for white paint system is between 61 % to 65 V% and this value is close to the transition point of capillary structure to funicular structure. Hence, in order to fabricate the superhydrophobic coating with the highest mechanical durability, particle volume percent should be in the range of 60V% to 70V%. Summary This data is the first in the literature to quantify superhydrophobicity and its durability. Previous work that w as reported by other groups only provided preliminary test s that are neither reproducible nor quantifiable. Baye et al trample d te sting samples with their shoes and use d this method to conclude durability of the coating Although they mentioned human weight is 90 kg, they missed many parameters such as pressure, roughness, abrasive material (sand/dirt on shoe) and type of loading, i.e. tangential shear vs. torsion. In a report by Xiu et al [46] the sample was abraded for only one cycle and the applied force is not stated. Therefore, in this paper, we developed a wear resistance test based on similar ASTM tests for coatings. Our samples show quantifiable wear resistance and superhydrophobic propertie s after 1000 abrasion cycles. Wear index is reported to help researchers to evaluate the rigidity of the coating, which depends on the solid loading of pigments. This work reports the first quantitatively tested superhydrophobic coating. Coatings have been made with various solid loadings of pigments. Superhydrophobicity was achieved for samples containing 65.2V% and 61.1V% of pigments. These coating showed superhydrophobicity after fabrication and continued to be superhydrophobic during the abrasion testi ng, well after 1000 abrasion cycles by metallurgy sand paper (1200C). The coating depletion + rate (CDR) is higher for a pendular structure of a coating and becomes less for denser structures. Despite the open pendular structure, the 65.2 V% has only losses of 15% from 1000 abrasion cycles. Both coatings could be painted on commercial products to provide

PAGE 53

53 superhydrophobic properties, thus keeping t he surfaces clean and dry. W e expect that it extends enhanced anti corrosion, anti fouling properties, and more. Superhydro phobic Black Paint Fabrication a nd Characterization Materials a nd Experimental Process Fabrication of superhydrophobic black pigments Iron oxide black matte was purchased online from Powdered Up Dolly. The processing starts with iron oxide parti cles being dehydrated in the oven at 120C, which are then dispersed in chloroform. Subsequently, heptadecafluoro 1, 1, 2, 2, tetrahydrodecyltrichlorosilcane, from Gelest Inc., was added to the iron oxide chloroform dispersion with the ratio 1ml : 1g iron o xide and treated for 1 hour. Afterwards, the dispersion was centrifuged and the chloroform was decanted. Drying of particles was done at 120C on a heating plate for 5 hours. The fluorinated black matte was obtained in this way. Binder blending Standard bi nder solution (SBS) was used for black paint fabrication, and the recipe is listed in white paint section. Preparation of coating samples with different V% To achieve black matte, fluorinated iron oxide was added to the SBS at different volume percent: 7 5% (with 2.26g fluorinated iron oxide added), 70% (with 1.78 fluorinated iron oxide added), 65% (with 1.45g fluorinated iron oxide added), and 60% (with 1.11g fluorinated iron lime glass slid es were coated and spun at 100 rpm by a spin coater. The slides were dried in air for at least 24 hours.

PAGE 54

54 Results a nd Discussion Initial Contact Angle Measurement In black paint system, the threshold to achieve superhydrophobicity was found between 60 V% to 65V% (shown in Figure 3 13) with contact angle increasing with more pigments added. Compared to threshold value of white paint, which is around 55%~60%, value of black paint is higher. The reason for this is that silica particles (white pigment) have mor e hydroxyl groups on the surface than that of the iron oxide particles (black pigment). This suggests that coverage of fluorosilane on silica is higher than on iron oxide, meaning that higher surface roughness is needed to achieve superhydrophobic regime i n iron oxide system. Eq. 1.10 shows a droplet to stay in Cassie Baxter state. This equation explains why the threshold value of black paint is higher than whit e paint. Figure 3 13 Initial contact angle of black paint with different V% black paint

PAGE 55

55 Black Paint Wear Resistance Test b y Using 1200C Sand Paper a s Abrader Figure 3 14 s hows how contact angle changes as abrasion cycles increase. Declining trends of t he 75V% and 70V% paints are more obvious than that of the 65% and 60% paints. Because higher V% yields more fragile structure, the contact angle of these four samples dropped below 150 after 400 cycles. Figure 3 14 Contact angle changes against abrasio n cycles increase black paint/ 1200C sand paper ( : 75 70V%, : 65 V % : 60 V % ) Sample V% : 60 V% : 65 V % 70 V % : 75 V% Slope of regression line of contact angle change 6 86 E 3 5 57 E 3 1 3.1E 3 14 57 E 3 Figure 3 15 List of contact angle trend black paint/ 1200C sand paper

PAGE 56

56 Figure 3 1 6 and Figure 3 17 exhibit weight loss (%) and CDR of black paint with different V%. Under abrasion of 1200C sand paper, weight loss and CDR of four samples were quite similar, which was around 5~6 %. Here, the explanation is that 1200C sand paper is too fi ne to destroy the polymer matrix so that only top layer of fluorinated iron oxide particles were removed. The retained polymer matrix was compressed by pressure from abrader loading (50 kPa). That is the reason why the contact angle kept declining and even tually reach the value that the pure PVDF PMMA mixed polymer possesses (The contact angle of PVDF PMMA mixed polymer is 100). Figure 3 16 Weight loss with different volume percent after abrasion black paint ( 70V%, :65 V%, : 60 V %) bla ck paint/ 1200C sand paper Figure 3 17 List of wear index, weight loss part per thousand, and slope of regression line for by varying the volume percent of pigments adding black paint/ 1200C sand paper Sample V% : 60 V% : 65 V % 70 V % : 75 V% Wear Index (mg/cycle) 0.011 0.012 0.01 0.014 Percentage of weight change to initial weight after 1000 cycles abrasion (%) 4.55 0.5% 6.29 %0.5% 5.9 %0.5% 5.28 %0.5% Slope of regression line (CDR) 5 01 E 3 5 7 E 3 5. 6 E 3 5 22 E 3

PAGE 57

57 Black Paint Wear Resis tance Test by Using 600 C Sandpaper as Abrader perspective. Because 1200C sand paper only removed the top layer of particles but the polymer matrix is still sturdy. So, we cho se 600C sand paper to be applied to black superhydrophobic abrasion test. Because 600C sand paper is rougher than 1200C, the goal of using 600C is to destroy polymer matrix layer by layer. With damaging of polymer matrix, we expect the contact angle should not change sharply but the CDR might be higher than the results abraded by 1200C. Th e outcomes shown in the Figure 3 18 and Figure 3 19 match our expectation. The contact angle after abrasion keeps fluctuating and the declining trend is close to zero. Rou gher sand paper can destroy the polymer matrix so new layer of fluorinated particles unveil and random packaging of particles contributes high roughness. Thus, the contact angle remain stable in this abrasion test. Figure 3 18 Contact angl e fluctuate with abrasion cycles increase black paint/ 600C sand paper ( : 75 70V%, : 65 V % : 60 V % )

PAGE 58

58 Sample V% : 60 V% : 65 V % 70 V % : 75 V% Slope of regression line of contact angle change 1.43E 3 2.29E 3 3.43E 3 5.71 E 4 Figure 3 19 Contact angle declin ing trend black paint / 600C sand paper Figure 3 20 and Figure 3 21 list weight loss and CDR of black paint under 600C sand paper abrasion. Compare to the data under 1200C sand paper abrasion. Weight loss increases significantly with rougher sand paper. 75V% sample lost 31% of weight, 70V% sample lost 2 6% and this value is 500% ~600% comparing to the weight lost under 1200C abrasion. This data prove s the explanation that polymer matrix damage s or not stro ngly influence s the wettability. Figure 3 20 Weight loss with different volume percent after abras ion black paint/ 600C sand paper ( : 75 70V%, : 65 V % : 60 V % )

PAGE 59

59 Sample V% : 60 V% : 65 V % 70 V % : 75 V% Wear Index (mg/cycle) 5 .6 x10 3 0.02 0.047 0.089 Percentage of weight change to initial weight after 1000 cycles abrasion (%) 3.96 0.5% 12 0.5% 26.08 0.5% 31.66 0.5% Slope of regression line (CDR) 3.98E 3 12E 3 25.8E 3 31.7E 3 Figure 3 21 List of wear index, weight loss part per thousand, and slope of regression line for by varying the volume percent of pigments adding blac k paint/ 600C sand paper Summary Black superhydrophobic paint was made successfully by mixing fluorinated iron oxide particles and SBS. By adjusting V% of adding pigments, threshold value was found between 60V%~65V%, and samples with 65V%, 70V %, 75V% ach ieved superhydrophobic ity after coating solidified. Two types of sand paper, which are 1200C and 600C, were used in Chapter 3 because CDR data shows that 1200C sand paper is too fine to destroy polymer matrix of black paint because the loss of weight for 4 samples are around 5~6%. Without destroy ing the polymer matrix, although decreasing the contact angle in 1200C abrasion test, four samples were in superhydrophobic regime after 400 cycles abrasion. Furthermore, 600C sand paper abrasion test expressed outcomes which are close to our expectation. Polymer matrix was destroyed layer by layer so that fluorinated particles which were buried in polymer matrix at beginning ascended to the top layer and formed random rough surface. This is the re ason why water contact angle was trivial in the test abraded by 600C sand paper. For proving this explanation, CDR data under 600C sand paper abrasion is much higher than 1200C. 75V% sample los t 31% weight after 1000 times 600C sand paper abrasion which i s 6 times higher than the results under 1200C. Superhydrophobic and durable black paint has been successfully fabricated with fluorinated iron oxide black matte and PVDF PMMA mixed polymer with 65 V%~75V% black pigments adding.

PAGE 60

60 Superhydrophobic Blue Paint Fabrication a nd Characterization Materials a nd Experimental Process Fabrication of superhydrophobic blue pigments Ultra marine blue matte was purchased from P owdered U p D olly. The processing starts with, blue matte particles being dehydrated in the oven at 120C and then dispersed in chloroform. Subsequently, heptadecafluoro 1, 1, 2, 2, tetrahydrodecyltrichloros ilcane, which is from Gelest Inc., was added to the ultramarine chloroform dispersion with the ratio 1ml : 1g blue matte and treated for 1h. Afterward s centrifuging the dispersion and decanting the chloroform follows. Drying of particles is done at 120C on a heating plate for 5hs. The fluorinated blue matte is obtained in this way. Binder blending Standard binder solution (SBS) was used for blue paint fabrication and the recipe is listed in white paint section. Preparation of pure blue coating sample s with different V% After binder blending, adding pigments which are Ultra marine blue matte with different volume percent which are 75% (with 1.04g fluorinated ultramarine adding), 70% (with 0.8g fluorinated ultramarine adding), 65% (with 0.64g fluorinat ed ultramarine adding), and 60% (with soda lime glass slide with 100 rpm rotation speed by spin coater. Then dry in air for 24 hrs. Preparation of white blue m ixed paint Blue#1 (B1) paint contains pure hydrophobized ultramarine 75V% as a superhydrophobicity contributor blend ed with the standard binder solution but paints B2 to B4 are fluorinated ultramarine adulteration in 65V% silica white paint. For e xample, B2 is 65 V% silica white paint blend ed with 0.1g ultramarine, B3 is with 0.2g ultramarine, and B4 is with 0.3g

PAGE 61

61 ultramarine respectively. Because of different amount of adulteration, we are able to develop various blue paints. Results and Discuss ion Initial Contact Angel Measurement In blue paint system, threshold value was found between 60V%~65V% (shown in Figure 3 22) and this number is almost identical to the value in black paint system. Random stacking empirical outcome can be used to explain why threshold value was detected in this range. Density of random close packing was found in the range of 56% 64% [33]. Above this value, polymer matrix distribution st arts to change (shown in Figure 3 4) from funicular to pendular. With this shif t r oughness of coating increa ses s uch that the contact angle also increases. Figure 3 22 Initial contact angle of blue paint with different V% Wear Resistance Test by Using 600C Sand Paper Blue Paint In abrasion test, 600C sand paper was selected to be the abrader in order to remove both particles and polymer matrix on the top layer. Interestingly, contact angle of blue paint decreases gradually wh ile testing. From the data in Figure 3 23 contact angle of 4 samples with different

PAGE 62

62 V% drops to 110 We speculate the reason is that the structure of blue paint is stronger than black paint or white paint so that 600C sand paper was not able to destroy the polymer matrix. As a means to observe steady contact angle under abrasion test, polymer matrix sho uld be erased layer by layer. Rougher sand paper is needed. Figure 3 23 Contact angle decreases with abrasion cycles increase blue paint/ 600C sand paper ( : 75 70V%, : 65 V % : 60 V % ) Figure 3 24. Contact angle decreasing trend of blue paint/ 600C sand paper Figure 3 25 shows the CDR and wear index of samples with 75V%, 70V%, 65V% and 60V% pigments adding. Under abrasion of 600C sand paper, weight loss and CDR of four samples are quite similar which are all around 5 ~6 % and this number is close to the loss of black sample under 1200C abrasion test. This consequence demonstrated the explanation in the Sample V% : 60 V% : 65 V % 70 V % : 75 V% Slope of regr ession line of contact angle change 0.039 0.046 0.042 0.043

PAGE 63

63 previous section. Wear resistance of blue paint is stronger so that even 600C sand paper was only able to remove particles s uch that the retained polymer was compressed by abrader loading and contact angle decli ne was observed Figure 3 25 Weight change against abra sion cycles increase blue paint/ 600C sand paper ( : 75 70V%, : 65 V % : 60 V % ) Sample V% : 60 V% : 65 V % 70 V % : 75 V% Wear Index (mg/cycle) 7.5 E 3 1.7E 3 4E 3 7.5E 3 Percentage of weight change to initial weight after 1000 cycles abrasion (%) 3.4 0.5% 2.38 0.5% 4.6 0.5% 5.9 0.5% Slope of regression line (CDR) 3 .4E 3 2 .3E 3 4 .6E 3 5 8 E 3 Figure 3 26 List of wear index, weight loss (%) and slope of regr ession line for by varying the v olume percent of pigments adding blue paint/ 600C sand paper

PAGE 64

64 White Paint Blended by Blue Pigments B1 is the pure blue paint with 75V% fluorinated ultramarine adding. B2~B4 are 65V% white paint with 0.1g, 0.2g, 0.3g fluorinated ultramari ne adding, respectively. Figure 3 27 show s the appearance of samples and initial contact angle measurements w ere also reported in Figure 3 27. B1 B4 expressed superhydrophobicity after coating was dried in air for 24hrs. With this effect, we know fluorinated color pigments can be blended together for color adjusting. Contact angle changing against abrasion cy cle s for B1 B4 was show in Figure 3 28 Trend of B1is similar comparing to the previous result. In samples B2 B4, with more blue matte adding, structure was getting weaker so that 600C sand paper can deplete the polymer matrix. Hence, contact angle were still above 150 after 1000 time abrasion. Figure 3 27 Appearances of B1 to B4 (Photo c ourtesy of author) Figure 3 28. DI water contact angle for B1~B4 samples. (Photo c ourtesy of author)

PAGE 65

65 Figure 3 29 Change of contact angle with increasing of abrasion cycles for white blue mixed paint system Summary Blue superhydrophobic paint was successfully fabricated by fol lowing the logic of new design. By varying the V% adding, threshold value to achieve superhydrophobicity was found between 60V% 65V% in blue pain t system. under 1200C sand paper nor 600C sand paper. This phenomen on is quite different from other 4 paints. The reason is that polymer matrix was not damaged by these two sand paper so that the lower level of particle s is still implant ed in polymer matrix. In doing so, roughness factor decreases while abrasion, so contact angle declined to intrinsic contact angle of PVDF PMMA mixed polymer. With rougher sand paper like 300C or even 120C, blue pai nt may be able to remain in superhydrophobic regime after 1000 times abrasion. To conclude, superhydrophobic and durable blue paint has been successfully fabricated with fluorinated ultramarine blue matte

PAGE 66

66 and PVDF PMMA mixed polymer with 65V%~75V% This dat a is also the first quantitative data to describe durability of superhydrophobic blue coating. Superhydro phobic Green Paint Fabrication a nd Characterization Materials and Experimental Process Fabrication of superhydrophobic green pigments Chromium oxide gr een matte was purchased from P owdered U p D olly. The processing starts with, chromium oxide green matte particles being dehydrated in the oven at 120C and then dispersed in chloroform. Subsequently, heptadecafluoro 1, 1, 2, 2, tetrahydrodecyltrichloros ilcane, which is from Gelest Inc., was added to the chromium oxide chloroform dispersion with the ratio 1ml : 1g green matte and treated for 1h. Afterward, centrifuging the dispersion and decanting the chloroform follows. Drying of particles is done at 12 0C on a heating plate for 5hs. The fluorinated green matte is obtained in this way. Binder blending Standard binder solution (SBS) was used for green paint fabrication and the recipe is listed in white paint section. Preparation of pure gre en coating samples with different V% After binder blending, adding pigments which are chromium oxide green matte with different volume percent which are 75% (with 2.27g fluorinated green matte adding), 70% (with 1.79 fluorinated green matte adding), 65% ( with 1.46g fluorinated green matte adding), and 60% lime glass slide with 100 rpm rotation speed by spin coater. Then dry in air for 24 hrs. Prepara tion of white green mixed paint Green #1 ( G 1) paint contains pure hydrophobized green matte 75V% as a superhydrophobicity contributor and then blend ed with the standard binder solution but paints

PAGE 67

67 G2 to G4 are fluorinated green matte adulteration in 65V% silica white paint. For example, G2 is 65 V% silica white paint blending with 0.1g fluorinated green matte adding, G3 is with 0.2g fluorinated green matte adding, and G4 is with 0.3g fluorinated green matte adding, respectively. The logic of white blue mix ed paint was follower to develop various green paints. Initial Contact Angle of Coating w ith Different V % Pigments Figure 3 30 H igher pigment volume percent yields higher initial contact angle green paint system Wear Resistance Test by Using 600C Sand Paper Green Paint Figure 3 31 p rovides the contact angle changing against abrasion cycles for green paint As the data shown, contact angle of coating fluctuated because the polymer matrix was destroyed and this phenomenon matched our expectation. 75V% gr een paint possessed 154 contact angle after 1000 times abrasion and other 3 samples were also in superhydrophobic regime.

PAGE 68

68 Figure 3 31 Contact angle fluctuates with abrasion cycles increase green paint/ 600C sand paper ( : 75 70V%, : 65 V % ) Sample V% : 65 V % 70 V % : 75 V% Slope of regression line of contact angle change 1E 3 0.00 2 0.0014 Figure 3 32 Contact angle changing trend of green paint/ 600C sand paper Figure 3 33 gives the weigh t change of samples, which are 75%, 70%, 65%, and CDR was calculated by regression line program with 99% confidence. The calc ulated value s are shown in the Figure 3 34 75V% one lost 9.26% of weight which is the highest among these samples because higher V% pigments adding gave fragile structure but yielded better wettability. From the facts of weight loss, we know the polymer matrix was destroyed so the wettability was steady due to new layer of particles ascended to the top.

PAGE 69

69 Figure 3 33 Weight change in percenta ge against abrasion cycles increase green paint/ 600C sand paper ( : 75 70V%, : 65 V % ) Sample V% : 65 V % 70 V % : 75 V% Wear Index (mg/cycle) 8E 3 8.5E 3 0.014 Percentage of weight change to initial weight after 1000 cycles abrasion (%) 6 .9 0.5% 6.4 0.5% 9.26 0.5% Slope of regression line (CDR) 6.7E 3 5.9E 3 8E 3 Figure 3 34 List of wear index, weight loss (%), and slope of regression line (CDR) for by varying the volume percent of pigments adding green paint/ 600C sand paper Whi te Paint Blended by Green Pigments G1 is the green paint with 75V% fluorinated chromium oxide green matte adding. G2~G4 were 65V% white paint with 0.1g, 0.2g, 0.3g fluorinated chromium oxide green matte adulterated, respectively. Figure 3 35 shows the appe arance of samples. Initial contact angle measurements were also reported in Figure 3 36 Depending on the results, G1~G4 expressed

PAGE 70

70 superhydrophobicity after coating was dried in air for 24hrs. Contact angle changing against abrasion cycles for G1 G4 was sh ow in Figure 3 36 All 4 samples possess superhydrophobicity after 1000 times abrasion by 600C sand paper. Figure 3 35 Appearances of G1 to G4, G1 is 75V% pure green paint, G2~G3 are green pigments adulterated white paint. (Photo c ourtesy of author ) Figure 3 36 Initial contact angle of G1~G4 (Photo c ourtesy of author) Figure 3 37 Change of contact angle with increasing of abrasion cycles for white green mixed paint

PAGE 71

71 Summary Green superhydrophobic paint was successfully made by following the lo gic of new design, which is the volumetric superhydrophobic coating. Because there is a trade off between wettability of coating and wear resistance, threshold value to achieve superhydrophobicity should be demonstrated. By varying the V% adding, threshold value to achieve superhydrophobicity was found between 60V% ~65V% in green paint system. Experiment for Contact angle change against abrasion cycles was done by Taber linear abraser with 600C sand paper as an abrader. This data shows that three sampl es, which are 65V%, 70V% and 75V%, are still in superhydrophobic regime after 1000 times abrasion. Weight loss of coatings were also measured and the CDR of these 3 samples was also calculated. 75V% loss 9.26% after 1000 times abrasion which means 75V% coa ting may survive up to 10000 times abrasion. Moreover, 70V% and 65V% lost only 5% after 1000 times abrasion which are more rigid than 75%. Fluorinated green matte also could be used to adulterate our white paint system in order to adjust color t o satisfy demanding circumstance s To conclude, superhydrophobic and durable green paint has been successfully fabricated with fluorinated chromium oxide green matte and PVDF PMMA mixed polymer with 65V%~75V% green pigments adding. This data is also the first quantitative data to describe durability of superhydrophobic coating. Superhydrophobic Red Paint Fabrication a nd Characterization Materials and Methods Fabrication of superhydrophobic red pigments Iron oxide red matte was purchased from P owdered U p D olly. The processing starts with, Iron oxide red matte particles being dehydrated in the oven at 120C and then dispersed in chloroform. Subsequently, heptadecafluoro 1, 1, 2, 2, tetrahydrodecyltrichlorosilcane, which is

PAGE 72

72 from Gelest Inc., wa s added to the iron oxide chloroform dispersion with the ratio 1ml: 1g red matte and treated for 1h. Afterward, centrifuging the dispersion and decanting the chloroform follows. Drying of particles is done at 120C on a heating plate for 5hs. The fluorina ted red matte is obtained in this way. Binder blending Standard binder solution (SBS) was used for red paint fabrication and the recipe is listed in white paint section. Preparation of pure red coating samples with different V% Adding fluorinated iron oxide red matte with different volume percent which are 75% (with 2.26g fluorinated iron oxide adding), 70% (with 1.78 fluorinated iron oxide adding), 65% (with 1.45g fluorinated iron oxide adding), and 60% (with 1.11g fluorinated iron oxide add ing). lime glass slide with 100 rpm rotation speed by spin coater. Then dry in air for 24 hrs. Preparation of white red mixed paint Red #1 (R1) paint contains 75V%pure hydrophobized red mattes as a superhydrophobicity contributor and then blend ed with the standard binder solution but paints R2 to R4 are fluorinated red matte adulteration in 65V% silica white paint. For example, R2 is 65 V% silica white paint blending with 0.1g fluorinated red matte adding, R3 is with 0.2g fluorinated red matte adding, and R4 is with 0.3g fluorinated red matte adding, respectively. Results and Discussion Initial Contact Angle Measurements Red Paint In red paint system, threshold value was also found betwe en 65V%~70V% and this value is close to the range of possible density of random close packing which is 56% 64% and complied with our expectation. Polymer distribution shifts from saturated to pendular with

PAGE 73

73 decreasing volume percent of polymer. Figure 3 38 gives the results that higher V% paint yields higher initial contact angle and this also fulfills our prediction due to the higher roughness factor in high V% system. Figure 3 38 Higher pigment volume percent yields higher initial contact angle red pa int system Abrasion Test by Using 600c Sand Paper Red Paint F igure 3 39 Contact angle fluctuates wit h abrasion cycles increase red paint/ 600C sand paper ( : 75 70V%, : 65 V % : 60 V% )

PAGE 74

74 Contact angle change against abrasion cycles incr ease was listed in the Figure 3 39 and we can see them fluctuate and the values were close to the initial contact angle of each of them after ab rasion. Explanation for other color paint system s is also fitting here. 600C sand paper was rough enough to destroyed polymer matrix so that new rough surface came out and hold supe rhydrophobicity after abrasion. S ample V% : 60 V% : 65 V % 70 V % : 75 V% Slope of regression line of contact angle change 0.004 8.6E 4 5.7E 4 8.6E 4 Figure 3 40 Contact angle changing trend of red paint/ 600C sand paper In red superhydrophobic paint system, 75V% paint lost 31% of weight after 1000 abrasion but CDR of red paint was twice of the other three samples. We speculate that polymer distribution shifted from funicular to p endular so that 75V% is much more fragile than others. Figure 3 41 Weight change in percentage against abrasion cycles increase red paint/ 600C sand paper ( : 75 70V%, : 65 V % : 60 V % )

PAGE 75

75 Sample V% : 60 V% : 65 V % 70 V % : 75 V% Wear Index (mg/cycle) 0.01 8.6E 3 0.02 0.07 Percentage of weight change to initial weight after 1000 cycles abrasion (%) 14 0.5% 12 0.5% 18.7 0.5% 35.5 0.5% Slo pe of regression line (CDR) 0.013 0.012 0.019 0.036 Figure 3 42 List of wear index, weight loss (%) and slope of regr ession line (CDR) for by varying the v olume percent of pigments adding red paint/ 600C sand paper White Paint Blended by Red Pigme nts R1 is the red paint with 75V% fluorinated iron oxide red matte adding. R2~R4 were 65V% white paint with 0.1g, 0.2g, 0.3g fluorinated iron oxide red matte adulterated, respectively. Figure 3 34 shows the appearance of samples. Initial contact angl e measurements were also reported in Figure 3 44 Depending on the results, R1~R4 possessed superhydrophobicity after coating was dried in air for 24hrs. Contact angle changing against abrasion cycles for R1 R4 was show in Figure 3 4 All 4 samples were in superhydrophobic regime after 1000 times abrasion by 600C sand paper. Figure 3 43 Appearances of R1 to R4, R1 is 75V% pure red paint, R2~R3 are red pigments adulterated white paint. (Photo c ourtesy of author)

PAGE 76

76 Figure 3 44 Initial contact angle of R 1 R4 (Photo c ourtesy of author) Figure 3 45 Change of contact angle with increasing of abrasion cycles for white red mixed paint Summary Red superhydrophobic paint was successfully fabricated by following the logic of new design. Because there is a tra de off between wettability of coating and wear resistance, threshold value to achieve superhydrophobicity should be demonstrated. By varying the V% adding,

PAGE 77

77 threshold value to achieve red superhydrophobicity was found between 65V% 70V % in red paint system. Experiment for contact angle change against abrasion cycles was done by Taber linear abraser with 600C sand paper as an abrader. 70V% and 75V% samples are still in superhydrophobic regime after 1000 times abrasion. Weight loss of coatings were also mea sured and the CDR of samples was also calculated. Because black and red paint are iron oxide based paint so the adhesion between particle and polymer is almost identical. Weight change after abrasion was similar to the data of black paint. To conclude, sup erhydrophobic and durable red paint has been successfully fabricated with fluorinated iron oxide red matte and PVDF PMMA mixed polymer with 65V%~75V% red pigments adding. This data is also the first quantitative data to describe durability of superhy drophobic red coating. Discussion a nd Understanding In Figure 3 46, trans itions point to achieve superhydrophobic ity were d iscovered between 60 V% to 70V% for four sorts of paints. Interestingly, pigments used for 4 sorts of paint were different which are i ron (II) oxide (black), iron (III) oxide (red), chromium (III) oxide and Ultramarine (blue) Figure 3 47 shows the structure of particle polymer composite with different ratio of particle. Structure shifts to funicular structure from capillary structure on ce particle volume percent is higher than 65% and contribute to higher wall roughness. 65V% is also the upper limit of random close packing density. Therefore, this dissertation demonstrated a general principle for volumetric superhydrophobic coating fabri cation. By adjusting the volume percent of particles, coating can attain superhydrophobic as long as particle volume percent is higher than 65V%. However, coating with higher particle volume percent yields a weaker structure. Therefore, 60 V% ~ 70V% is the most appropriate to balance wettability and durability.

PAGE 78

78 Figure 3 46 Correlation of initial contact angle and volume percent of particles Figure 3 47 Different ratio of particle and polymer turns out different structure Chapter Conclusion In Chapter 3, five sorts of durable superhydrophobic paint s were invented by blending selected fluorinated color matt e and standard binder solution. By adjusting the volume percent of

PAGE 79

7 9 added pigment, threshold to achieve superhydrophobic was found for 5 sorts of pain t. The thresholds are in the range of 60 V%~ 70 V% which is the possible maximum packing density of random packaging Once particle volume ratio is above this range, structure of coating turned from thin film like structure to fluffy. With fluffy structure, r oughness factor strongly increases. However, strength of structure descends dramatically so CDR is around 200% than the thin film like structure. Nevertheless, polymer is distributed between particles and this is why fluffy structure retains decent durability. On the other hand, t his work also demonstrates the ability to use modified ASTM standards to characterize the durability of superhydrophobic surfaces. The data that needs to be collected is the water contact angle change vs. the number of abra sion cycles, the weight loss vs the number of abrasion cycles The hope is that this approach can be the basis for a new ASTM standard.

PAGE 80

80 CHAPTER 4 FABRICATION OF DURABLE SUPERHYDROPHOBIC AND TRANSPARENT COATING VIA SILICA SOL GEL COVER LAYER Introduction T he purpose of Chapter 4 is to investigate a new method to strengthen the surface feature of a transparent and superhydrophobic coating by using monodisperse nanoparticles and silica sol gel cover layer. The material chosen in Chapter 4 is silicon dioxide ( SiO2) which is synthesized from tetraethyl orthosilicate (TEOS) by the Stber process. Silica sol was also synthesized from TEOS with an acidic catalyst and played a role of binder in Chapter 4 To achieve superhydrophobicity, heptadecafluoro 1 1 2 2 tetr ahydrodecyl trichlorosilane was applied on the surface of silica cover layer and silica particles for improvement of surface chemistry. Contact angle change against abrasion cycles and transmitta nce are reported in Chapter 4 Background To achieve transpare nt and superhydrophobic surface, light scattering theory was referred to explain how to build surface feature s but reduce light scattering. Light Scattering Theory Formal light scattering theory can be categorized in two frameworks. One is the theory of Rayleigh scattering (after Lord Rayleigh) [58], [59] and another is Mie scattering (after Gustav Mie) [60] [62] Rayleigh is applicable to small, dielectric (non absorbing), spherical particles. Mie scattering has no size limitations and can be used to describe most spherical particle sca ttering systems. Rayleigh scattering and Mie scattering are used in different criteria described (4 1)

PAGE 81

81 Dep for spheres) In Chapter 4 we are going to develop a coating that is transparent in the visible light range (400 700nm) and the size of nanoparticle is 50nm to 60nm. Therefore, Mie scattering is a more reasonable model to illustrate the scattering behavior in this proposal. For optimizing the superhydrophobic property, raising the surface roughness is required. However, increasing of the feature size of the surface causes scattering to be more and more conspicuous. As mentioned above, the Mie scattering theory is commonly used to describe the interaction between the surface roughness and incident visible light. According to Mie theory, the scattering cross section ( C sca ) is given by: (4 2) Where, the d is t he particle diameter and the a n and b n are Mie coefficient of the order n, which are related to the material property. C sca is proportional to d 2 however, surface features a re necessary for superhydrophobicity. It expresses there is upper limit of transparency with which the coating can still perform superhydrophobicity. Silica Nanoparticles Synthesis v ia Stber Process Stber process is a common process for the generation of monodisperse nano silica particles. This process was published in 1968 by Werner Stber et al [63] Briefly speaking, silicon alkoxides l ike tetramethoxysilane (TMOS), tetramethoxysilane (TEOS), etc. as the

PAGE 82

82 precursor were added to a low molar mass alcohol such as ethanol or methanol and small amounts of ammonia were used as a catalyst. The general steps are: 1. Hydrolysis The hydrolysis reacti on is : (4 3) 2. Polymerization (4 4) (4 5) Figure 4 1 Polym erization behavior of aqueous silica. In basic condi tion. A ) particles grow in size with decrease in number; however, B ) in acidic condition or in p resence of flocculation salts particles tend to agglomerate into three dimensional networks and form gels. F rom Iler [64]

PAGE 83

83 S ilicic acid solutions slowly become thicker and fina lly gel, and most researchers prior to 1979 believed that Si(OH)4 polymerized into siloxane and cross linked like other organic polymers [64] However, Iler reported that there is no relation or analogy between silicic acid polymerized in an aqueous system and condensation type organic polymers. Instead, silicic acid polymerizes into discrete par ticles that in turn aggregate into chains and networks as first recognized by Carmen. According to Iler [64] polymerization occurs in 3 stages: 1. Polymerization of monomer to form particles 2. Growth of the particles. 3. Linking of particles into chains, then networks that extend throughout the liquid medium, thickening it to a gel. p H Dependence In terms of silica polymerization behavior, pH value plays a s ignificant role, and is discussed in detail in the following statements. There are three pH domains of polymerization process reported by Iler which are < pH 2, pH 2 7 and > pH7. The reasons why Iler selected pH2 and pH7 as boundaries is that the point o f zero charge (PZC) and isoelectric point (IEP) are in the range of pH1~pH3. PZC means the surface charge is zero and IEP means electrical mobility of the silica particles is zero. pH 7 is a boundary because the silica particles are noticeably ionized above pH7 and the particles grow without aggregation and gelation. The main mechanism of the Stber process is in the range of pH7 to pH10. Polymerization above ph7 Above pH 7, which is the route B in the Figure 4 1, polymerization takes place in tw o nucleophilic reaction s :

PAGE 84

84 (4 6) (4 7) Nevertheless, condensed species will probably be ionized and therefore become repulsive to each other. Hence, growth is mainly caused by the addition of monomers to more highly condensed particles rather than by particle aggregation. Moreover, due to the greater solubility of silica and the greater size dependence of solubility above pH7, growth of the primary particles continue s by Ostwald ripening Particles grow rapidly to a size that depends mainly on the temperature. (Particles grow in larger size with higher temperature because of the higher solubility of silica). Since growth occurs by the dissolution of smaller particles and deposition of soluble silica on larger particles, the growth rate depends on the particle size distribution [65], [66] Fundamental o f Sol Gel Dip Coating Sol gel dip coating is a conventional thin film deposition process. Compare to other thin film deposition technique such as sputtering, evaporation, or chemical vapor deposition (CVD), dip coatin g relatively needs less equipment and is less costly. Scriven [38] divided dip coating process to 5 steps which are immersion, start up, deposition &drainage, drainage, solvent evaporation. Final film thickness is determined by six forces [67], [68] which are 1) viscous drag upward on the liquid by the moving substrate 2) force of gravity, 3) resultant force of surface tension in the concavely curved meniscus 4) inertial force of the boundary layer liquid ,5) surface tension gradient, and 6) the disjoini ng or conjoining pressure. From the report written by Strawbridge and James [69] they determined the relationship between silicate solution viscosity and thickness. The trend was found that higher viscosity results in thicker film in a fixed withdrawal speed. Here is why we set silicate sol V% as a parameter and try to find threshold

PAGE 85

85 value of film thickness which possess relative strength but not fully bury the silica nanoparticles layer. Materials a nd Methods Silica nanoparticles synthesis (stber process) Stber process was used to synthesize silica nanoparticles with 40nm diameter. 8.33g of tetra ethyl silicate (TEOS), 5g of de ionized water, and 0.98g of 0.28N aqueous ammonium hydroxide solution were added to 100ml 99% ethanol and agitated for 24hours at 50C. This process generated monodisperse silica nanoparticles of ~40 nm, as measure d by SEM. Silica sol gel synthesis With acidic condition catalyzed, silica precursor formed a thin film structure, which differed from forming monodisperse nanoparticles in basic c ondition. The reactants are de ionized water 28.8g, ethanol 18.4g (assay: 99%), TEOS 20.8g (assay: 99%), 1ml 1M Hydrogen chloride solution. The total molar ratio is TEOS: water: Ethanol is 1:16:4. After sol gel solution is prepared, the silica sol gel and ethanol was mixed with different volume percent s which are 1%, 2%, 3%, 4%, and 5%. Silica nanoparticles deposition The solvent for dispersing nanoparticles was ethanol. Best results were achieved with a sol i d loading (SL) of 0.2% (0.1 g / 50 ml), 0.4% (0 .2g/50ml), and 0.6% (0.3g/50ml). Dispersion was achieved using ultrasound. After the dispersion is prepared, repeated dip coating up to 5 times was tested. A minimum of two dip coats are needed to achieve the minimum roughness for superhydrophobic behav ior (after all steps are completed) More than 5 cycles can also be done, however, the higher the number of cycles the less transparent the samples will be.

PAGE 86

86 Silica sol gel deposition Base on the result shown in the last paragraph, a minimum of two dip coat s are needed to achieve the minimum roughness for superhydrophobic behavior (after perfluoro silane coating completed). Glass slides with nanoparticles on surface were dipped in silica sol ethanol solution with different ratio (1%~5%). Then withdraw n at a speed of 1.5cm/1s by dip coater and were dried in air for 24hrs. Self assembled monolayer deposition hydrophobization Chemical used for third deposition layer was heptadecafluorodecyltrichlorosilane purchased from Gelest Inc. However, there are other chemicals which could contribute the similar property. For example, fluorinated alkyl silane and alkyl silane (greater than C8 is preferable). The third layer has been done successfully with the concentration 0.2% ~0.5% of fluorinated silane in chlor oform. Results a nd Discussion Initial Contact Angle Measurement Figure 4 2 C ontact angle image for sample with 69V% of particle (Photo c ourtesy of author) Varying concentration of silica sol results in different thickness of cover layer. In our prediction, this cover layer should be thin enough to prevent burring silica nanoparticle layer. Howe ver, if this layer is too thin, the mechanical strength enhancement would be insignificant. Threshold value was found at 60V% to 70V% with drawing speed 1. 5cm/1s of dipped coater.

PAGE 87

87 Figure 4 2 is the 69V Hart goniomete r. Initial contact angle of 69V % samples is 1532. C ontact Angle Change a gainst Abrasion Cycles Figure 4 3. Contact angle change with wiping cycles increase for samples with different silica particles volume percent ( : 87V%, : 77V%, :69V%, : 62.5V%, :57V% ) In order to understand the wear resistance of these transparent superhydrophobic samples d urability test was run by linear abraser model 5700 manufactured by TABER industry and the abrasive is windshield wi per manufactured by BOSCH and loading is 20g. This loading is close to the value that wind shield wiper applied on windshield Fig ure 4 3 lists change of contact angle (CA) with different wiping cycles for samples with particle volume percent, which is fro m (57V% to 87V%) As we can see, after 10 cycles wiping, CA of weak coating samples drop, e.g. 87V% and 77V %, to around 115 which is the intrinsic contact angle of heptadecafluorodecyl trichlorosilane. It means that the surface roughness has been destroye d. By contrast, durable coating, e.g. 62 V% and 69V %, could resist at least 70 wiping cycles and contact angle is still

PAGE 88

88 above 150. This is the threshold value we are seeking and fulfill our prediction which is 60V% to 70V% Transmittance Measurement Figure 4 4 Transmittance vs. wavelength with black glass, weak surface coating, and durable surface coating Transmittance was measured by the UV/Visibl e Perkin Elmer Lambda800. Figure 4 4 shows the transmittance (T %) of the durable ( 69V % ) and weak ( 87 %) coating samples compared to the blank refer ence glass s lide. From the Figure 4 4 weak coating s have 98% t ransmittance in the visible light wavelength (400 700nm). However, durable coating s only possess 82%~90% transmittance. Although there is a 10% discrepancy between these two samples, Figure 4 5 shows the transparenc y observed by the bare eye. The word on the sheet still distinguishable through two kinds of coating.

PAGE 89

89 Figure 4 5 Camera photo for weak (87V%) and durable (69 %) coating (Photo c ourte sy of author) Summary Transparent superhydrophobic coating was attained by silica nanoparticles stacking and then further undergoing hydrophobization process. Other reports also achieved transparent superhydrophobic coating with similar approaches. How e transparent superhydrophobic coating because particle layer s should be stack ed regularly and thickness should be small. Any particle agglomeration or cluster strongly impact s the transmittance of coating because of light scattering. In Chapter 4 we provide an idea about securing nanoparticle stacking by covering a layer of silica gel. This silica sol gel layer should be present along the surface of nanoparticle. If too thin, fortification of structure is not obvious. Conversely, if too thick, roughness factor will decrease dramatically and superhydrophobicity will vanish. Concentration of silica sol was adjusted to control the thickness of silica cover layer. A durable superhydrophobic coating was attained an d this coating remained superhydrophobic until 80 times of abrasion which is 500%~600% enhancement comparing to weak coating.

PAGE 90

90 CHAPTER 5 FABRICATION OF DURABLE SUPERHYDROPHOBIC AND TRANSPARENT COATING VIA SILANE COUPLING AGENTS Introduction In Chapter 4 sol gel layer was introduced to cover the deposited silica nanoparticles and intend ed to improve strength of surface feature. However, sol gel cover layer is only a physical enhancement which means that there is no chemical reaction occurring between cov er layer and deposited particles. In Chapter 4 silane coupling agent is brought to be a linker between nanoparticles and whole coating material could be regarded as a particles oligomer composite. This design is similar to the concept of dura ble superhydrophobic paint. However, transparency issue results in a complicated fabrication process because particle agglomeration strongly influence s the light scattering yield. So transparent superhydrophobic coating s are not being able to buil d up in one step l ike non transparent system. In Chapter 5 3 mercappropyl trimethoxysilane (MPTMS) was used as the silane coupling agent in order to connect each particle Silica nanoparticles were chosen to be surface roughness contributor. After reacte d with MPTMS, silica nanoparticles would turn to thiol group terminated and named as M particles. Glass slide was also treated with MPTMS and named as M Glass. Multilayer M particles were deposited on M glass and whole system was oxidized by hydrogen perox ide and thiol disulfide reaction was triggered by appropriate catalyzed environment. Thiol disulfide reaction occurred between M particles and particle glass slide. An oligomer particles composite was achieved in this method. Ultimately, heptadecafluoro 1, 1, 2, 2, tetrahydrodecyltrichlorosilcane was used to hydrophobized surface. Strength enhanced translucent superhydrophobic coating was attained.

PAGE 91

91 Back ground Silane Coupling Agents Silane coupling agents have been used to bond organ ic and inorganic mate rial. Figure 5 1 is the general formula of silane coupling agents and there two termination s in silane coupling agent formula which are organic functional group (R side) and hydrolyzable group (X side). Typical X side functional groups are alkoxy, acyloxy, halogen or amine and this side aims to the hydroxyl group ( OH) on the surface of metal oxide. These leaving groups possess different dissociation energ ies and byproducts. In Figure 5 2, Gelest Inc. listed dissociation energ ies for common leaving groups and researchers could select desired X side depending on experimental requirement. In general, reactivity decreases in the order: Si NR2 > Si Cl > Si NH Si > Si O2CCH3 > Si OCH3 > Si OCH2CH3 [70] On the other hand, selection s of R side are bountiful such as acrylate, epoxy amine, or mercapto etc. With R side existing, plenty of chemical reaction could be triggered by specific oxidation or catalyzed environment. Figure 5 1 Common formula of silane coupling agents Figu re 5 2 Dissociation energy of X Side leaving group, from Gelest Inc. [41].

PAGE 92

92 Strategy to Bond Nanoparticles a nd Glass Surface Figure 5 3 Schematic of a silicon oxide particle bonded to glass surface via oligomer chain. Because of the versatility of R s ide of silane coupling agents, we could choose any two kind of silane which can react to each other. For example, amine epoxide, thiol epoxide, or thiol thiol. Here, mercaptopropyl trimethoxysilane (MPTMS) was selected to synthesize thiol t erminated particle s or glass slide surface. Figure 5 2 illustrates the oligomer chain formation of glass particle, particle particle interface. Particles and glass slide were pre treated with MPTMS, and then thiol terminated particles were deposited on the thiol terminated glass slide. Subsequently, immerse whole system into hydrogen peroxide oxidation bath and thiol disulfide reaction would be activated and disulfide bond would be formed between particles and particle glass interface. Figure 5 4 Schema tic of thiol disulfide bond formation between silica particle and glass slide

PAGE 93

93 Thiol disulfide reaction Masayuki et al [71] claimed a n oxidation environment and catalyst for benzyl mercaptan to dibenzyl disulfide. In the report, thiol disulfide reaction was activated by hydrogen peroxide ethyl acetate solution. They also reported 3 catalysts and corresponding yield s and reaction time s Relying on their results, NaI was chosen as a catalyst in our thiol disulfide reaction. Conjugation of thiol group after oxidation In Figure 5 4 [72] thiol (R SH) can be oxidized by two electrons to sulfeni c acid (RSOH). Furthermore, R SOH can form disulfide bond with other thiol or react with another sulfeni c acid an two thiol terminated particles or of thiol terminated particle and glass. Durability of coating was enhanced by these inner chemical bonds like Figure 5 2. On the other hand, from the Figure 5 4, with excess oxidant, sulfeni c acid could be further oxidized to sulfinic acid (RSO2H) or even sulfonic acid (RSO3H). There is hydroxyl group existing in these three groups, so further hydrophobization process still can be conducted. Figure 5 5 Formation and reactions of sulfenic acid [72]

PAGE 94

94 Materials a nd Methods Silica nanoparticles synthesis (Stber process) Stber process was u sed to synthesize silica nanoparticles with 40nm diameter. 8.33g of tetra ethyl silicate (TEOS), 5g of de ionized water, and 0.98g of 0.28N aqueous ammonium hydroxide solution were added to 100ml 99% ethanol and agitated for 24hours at 50C. This process g enerated monodisperse silica nanoparticles of ~40 nm, as measure by SEM. Preparation of thiol terminated silica nanoparticles 40nm silica nanoparticles were dispersed in acetone by ultra sonication for 1 hr. and the ratio of silica particles in acetone wa s 0.2g in 50ml acetone. 100l MPTMS was added into silica dispersion and waited for 1hr. Thiol terminated silica particles were obtained in thi s way and named as T particles. MPTMS was purchased from Sigma Aldrich with 99% concentration. Preparation of thi ol terminated glass slide Glass slide was immersed in isopropanol and ultrasonicated for 30mins and the goal of this procedure is to clean contamination. Furthermore, glass slide was immersed in piranha solution for 30 mins and then flushed by DI water. Th e goal of piranha solution is to oxidize glass surface and enlarge the density of hydroxyl group on the silica particles. By doing this, more MPTMS could be bonded on the SiO2 particles and this results in more silane bonding chains forming in whole coatin g material. After treat ing with piranha solution, glass slide was immersed in 30ml acetone and 100l MPTMS was added and waited for 30mins. Dr ied at 120 in an oven for 15mins and contact angle of glass slide was measured here to verify MPTMS bonding. Glass slide was named T glass after water contact angle was over 50 which is the empirical value that other reports said.

PAGE 95

95 Deposit T particles on T glass 0.2g T particles were dispersed in acetone and ultrasonicated for 1 hr. Afterward, T glass slide w as dipped into T particle dispersion and withdrawn with s peed 85mm/min.T his process was repeated for 3 times in order to establish sufficient roughness Then sample was dried in air for 1hr Thiol disulfide oxidation Sample was dipped into ethyl acetate so lution with varied amount of NaI 1mol% aqueous solution and hydrogen peroxide. The reaction time was 30 mins. Concentration of NaI aqueous solution and H 2 O 2 is strongly affect whether the thiol disulfide bond can be activated or not and corresponding re sults were listed in the following paragraphs H ydrophobization Samples were dipped into hept adecafluorodecyltrichlorosilane chloroform solution with ratio 0.2% ~0.5%. Chemical used for hydrophobization was purc hased from Gelest Inc. Reaction time is 30 min s and in room temperature. Then, sample was dried in 120C oven for 1hr. Results a nd Discussion Wear Resistance of Samples with Different Oxidation Condition After T particles were deposited on T glass, thiol to disulfide reaction was conducted. However, b ecause oxidation environment was unknown yet, reaction time and concentration are the parameters and a series of experiment s have been done and reported in the Figure 5 6 and Figure 5 7. In Figure 5 6, reaction time was set as 24 hrs. and concentra tions of H 2 O 2 and NaI are varied and shown in this formula: Amount of EtAC was fixed to 30ml and X means the adding amount of 1mol% NaI aqueous solution. Y presents the adding amount of 30% hyd rogen peroxide. After 24hrs reaction,

PAGE 96

96 samples w ere treated by fluorinated silane in chloroform solution and dried in 120 oven Water contact angle was measured. In Figure 5 6, ratio of X : Y was anchored in 1:1 but the ir concentration was adjust ed. From the results, 4 samples show unstable contact angle. Basically, coatings were wiped out in 10 abrasion cycles although they possess superhydrophobicity at beginning. We hypothesized the reaction time was too long so the reaction time was re duced to 30mins. The outcome is shown in Figure 5 7. Once the reaction time was reduced to 30mins, coating was sturdier than samples with 24hrs reaction time. Figure 5 8 shows how contact angle decreases against wind shield wiper abrasion Sample s with 30 mins oxidation stay superhydrophobic until 40 cycles and contact angle drops to 110 after 70 cycles which means surface structure was not ruined totally until 70 cycles. Strength of surface structure was elevated by silane coupling agent. Figure 5 6 D iverse X, reaction time 24hrs Figure 5 7 R educed oxidation time enhanced the durability of coating reaction time 30 mins

PAGE 97

97 Figure 5 8 action time: 24hrs; : X: 50l, Y: 50 l, reaction time: 30mins) Summary Silica nanoparticles were treated by MPTMS and turned to thiol termination. With this functionality, thiol disulfide reaction could be triggered in specific oxidation condition. Stren gth of coating could be enhanced by disulfide bond on particle particle interface and particle glass interface. This idea the similar to our durable superhydrophobic coating. W hole coating is fortified by inner polymer web like structure. After hy drophobization, fluffy structure became superhydrophobic and with fair strength which can possess superhydrophobicity after 70 times abrasion by wind shield wiper. This is the first quantitative data to describe the wear resistance of transparent superhydr ophobic coating. With this idea, other sorts of silane coupling agent s also could be used to construct inter particle connection.

PAGE 98

98 CHAPTER 6 CONCLUSION versatile properties such as self cleaning, anti fouling, and ice phobicity. However, after many years of development, researcher s discovered SH material could only be fabricated in small scale and the structure was very vulnerable. The reason is that surface roughness is an essential factor to achieve superhydrophobicity. Although some reports claimed durable superhydrophobic material has been made, there was not a standard test to quantify the durability withstand wear Therefore, this dissertation provides a recommendation for the standardization of how wear resistance measurements should be taken for superhydrophobic materials, in reference to ASTM standards (ASTM D4060 14). Moreover, in order to prevail over durability issue of superhydrophobic material t his dissertation proposed a novel design which differs from traditional ways. A volumetric superhydrophobic coating was introduced to overcome the adversity of superhydrophobic material F luorinated particles w ere secured by polymer binder in funicula r structure and whole coating became fluffy and provided high roughness Our system is based on a polymethyl methacrylate polyvinylidene difluoride (PMMA PVDF) polymer blend, acting as a thermoplastic binder, and hydrophobized metal oxide particles, wh ic h develop surface roughness. By varying the V% of pigments, thresholds to achieve s uperhydrophobicity was demonstrated in the range of 60V% to 70V% particle volume percent. This range is the transition point between capillary structure to funicular struct ure and the maximum packing density of random close packing. A dramatic change of CDR was also observed in this range to prove the explanation of structure transition. Higher V% of pigments results in a weaker structure but possesses higher initial contact angle. So there is a trade off here

PAGE 99

99 researchers know which V% of pigment should be added and this will turn out a superhydrophobic coating with sturdiest structur e In terms of durability of coating, samples with 60%~70% V% of pigments expressed lowest CDR and could resist 1000 abrasion cycles by metallurgy sand paper and order to strengthen the applicability, formulating this coating as a paint allows for applicati on in to large areas, and the ability to select color, which are white, black, blue, green and red. On the other hand, another shortcoming of S H material is the transmittance This dissertation followed the consequences in the durable paint fabrication system and substitute pigment to monodisperse silica particle and binder to inorganic silica gel. Threshold to achieve superhydrophobicity was also found in the range of 60V% to 70V%. Sample 62V% and 69V% retained in superhydrophobic regime in after 80 ti mes abrasions by windshield wiper. This dissertation provides two measurements to quantify the durability of superhydrophobic material and a novel design to fabricate the durable superhydrophobic material as well. We hope this versatile material could be u sed widely in the future.

PAGE 100

100 LIST OF REFERENCES [1] J. Phys. Condens. Matter vol. 17, no. 9, pp. S639 S 648, Mar. 2005. [2] Water Langmuir vol. 12, no. 9, pp. 2125 2127, Jan. 1996. [3] Langmuir vol. 20, no. 6, pp. 2405 2408, Mar. 2004. [4] J. Am. Chem. Soc. vol. 135, no. 2, pp. 578 81, Jan. 2013. [5] A. Tuteja, W. Choi, M. Ma, J. M. Mab ry, S. A. Mazzella, G. C. Rutledge, G. H. Science (80 ). vol. 318, pp. 1618 1622, Dec. 2007. [6] Ind. Eng. Chem. vol. 28, no. 8, pp. 988 994, 1936. [7] S. R. Coulson, I. Woodward, J. P. S. Badyal, S. A. Brewer, C. Willis, P. Down, and S. S. J. Phys. Chem. B vol. 104, pp. 8836 8840, 2000. [8] R. Dufour, M. Harnois, hysteresis origins: Investigation on super Soft Matter vol. 7, no. 19, p. 9380, 2011. [9] Resistant Coatings on Langmuir vol. 28, no. 31, pp. 11391 9, Aug. 2012. [10] Cleaning Properties of Artificial Superhydrophobic Surfa Langmuir vol. 21, pp. 956 961, 2005. [11] Biofouling vol. 22, no. 5 6, pp. 339 60, Jan. 2006. [12] R. J. Klein, P. M. Bie Super Hydrophobic Surfaces with Nano Zeitschrift fr Met. vol. 94, no. 48, pp. 377 380, 2003.

PAGE 101

101 [13] al Lotus leaves Soft Matter vol. 5, no. 7, p. 1386, 2009. [14] surface Preliminary ass Science and Technology of Advanced Materials 2005, vol. 6, no. 3 4 SPEC. ISS., pp. 236 239. [15] P hys. Fluids vol. 21, no. 8, 2009. [16] Adv. Mater. vol. 19, pp. 3423 3424, 2007. [17] Proc. Nat l. Acad. Sci. USA vol. 105, no. 47, pp. 18200 5, Nov. 2008. [18] Europhys. Lett. vol. 47, no. 2, pp. 220 226, 2007. [19] Reports Prog. Phys. vol. 68, no. 11, pp. 2495 253 2, 2005. [20] Colloids and Surfaces A: Physicochemical and Engineering Aspects 2002, vol. 206, no. 1 3, pp. 41 46. [21] the cassie baxter state Langmuir vol. 30, no. 8, pp. 2061 2067, 2014. [22] Mater. Sci. Eng. R Reports vol. 72, no. 10, pp. 189 201, 2011. [23] Soft Matter vol. 4, no. 2, p. 224, 2008. [24] s and coatings: a Reports Prog. Phys. vol. 78, no. 8, p. 086501, 2015. [25] Langmuir vol. 23, no. 13, pp. 7293 7298, 200 7. [26] Langmuir vol. 25, no. 5, pp. 3260 3263, 2009.

PAGE 102

102 [27] eparation of transparent Adv. Mater. vol. 11, no. 16, pp. 1365 1368, 1999. [28] A. Nakajima, K. Hashimoto, T. Watanabe, K. Takai, G. Yamauchi, and A. Fujishima, parent superhydrophobic thin films with self Langmuir vol. 16, no. 17, pp. 7044 7047, 2000. [29] H. M. Shang, Y. Wang, S. J. Limmer, T. P. Chou, K. Takahashi, and G. Z. Cao, based films, Thin Solid Films vol. 472, no. 1 2, pp. 37 43, 2005. [30] fingerprint Chem. Commun. (Camb). vol. 49, no. 66, pp. 7310 2, 2013. [31] S. Hhne, C. Blank, A. Mensch, M. T hieme, R. Frenzel, H. Worch, M. Mller, and F. Macromol. Chem. Phys. vol. 210, no. 16, pp. 1263 1271, 2009. [32] robust superhydrophobicity Nanotechnology vol. 21, no. 15, p. 155705, 2010. [33] abrasion resistance of transparent super hydro phobic coating by combining crater like Mater. Sci. Eng. B Solid State Mater. Adv. Technol. vol. 161, no. 1 3, pp. 36 39, 2009. [34] Healing Superhydrophobic Coatings Angew. Chemie vol. 122, no. 35, pp. 6265 6269, 2010. [35] Bioinspir. Biomim. vol. 2, no. 4, pp. S126 S134, 2007. [36] J. Z one Adv. Funct. Mater. vol. 18, no. 22, pp. 3662 3669, 2008. [37] ple method for the preparation of superhydrophobic PVDF Appl. Surf. Sci. vol. 255, no. 8, pp. 4479 4483, 2009. [38] nano and hierarchical structures for superhydrophobicity, s elf Philos. Trans. A. Math. Phys. Eng. Sci. vol. 367, no. 1894, pp. 1631 1672, 2009.

PAGE 103

103 [39] X. Deng, L. Mammen, H. Science (80 ). vol. 335, no. 6064, pp. 67 70, 2012. [40] Nano Lett. vol. 9, no. 1, pp. 501 505, 2009. [41] Z. Cui, Q. Wang, Y. Xiao, C. Su, and Q. Chen, Appl. Surf. Sci. vol. 254, no. 10, pp. 2911 2916, 2008. [42] Durable Superhydropho Adv. Mater. vol. 23, no. 5, pp. 673 678, 2011. [43] M. Manca, A. Cannavale, L. De Marco, A. S. Aric??, R. Cingolani, and G. Gigli, nanoparticles based sol ge Langmuir vol. 25, no. 11, pp. 6357 6362, 2009. [44] thermally stable PDMS Appl. Surf. Sci. vol. 339, pp. 94 101, 2015. [45] Phys. Chem. Chem. Phys. vol. 14, no. 30, pp. 10497 10502, 2012. [46] healing superhydrophobic and superoleophobic surfaces from fluorinated decyl polyhedral Angew. Chemie Int. Ed. vol. 50, no. 48, pp. 11433 11436, 2011. [47] and oil durable superhyd rophobic J. Colloid Interface Sci. vol. 413, pp. 112 117, 2014. [48] prepared by dual layer me thod for anti corrosion and self Colloids Surfaces A Physicochem. Eng. Asp. vol. 490, pp. 182 188, 2016. [49] filter paper for oil water separation prepared by Appl. Surf. Sci. vol. 313, pp. 304 310, 2014. [50] J. Appl. Phys. vol. 114, no. 12, 2013. [51] W. Conshohocke North vol. 06, pp. 6 8, 1995.

PAGE 104

104 [52] due to evaporation in a partially wet granular Int. J. Numer. Anal. Methods Geomech. vol. 36, no. 7, pp. 918 943, 2012. [53] close packing limits for monodisperse and Soft Matter vol. 10, pp. 3826 41, 2014. [54] F. A.L. Dullien, Porous Media Fluid transport and pore structure 1992. [55] Powder Technol. vol. 84, no. 3, pp. 199 205, 1995. [56] J. Stat Phys. vol. 131, no. 4, pp. 567 573, 2008. [57] J. Phys. D. Appl. Phys. vol. 2, no. 6, pp. 863 866, 2002. [58] Phys. Today vol. 35, no. January, pp. 42 48, 1982. [59] Appl. Opt. vol. 34, no. 15, pp. 2765 2773, 1995. [60] Appl. Opt. vol. 43, no. 9, pp. 1951 1956, 2004. [61 ] Am. J. Phys. vol. 53, no. 10, p. 955, 1985. [62] light Appl. Opt. vol. 34, no. 31, pp. 7410 7418, 1995. [6 3] J. Colloid Interface Sci. vol. 26, no. 1, pp. 62 69, 1968. [64] R. K. Iler, The chemistry of silica: solubility, polymerization, colloid and s urface properties, and biochemistry 1979. [65] gel dip Thin Solid Films vol. 201, no. 1, pp. 97 108, 1991. [66] C. J. Brinker and G. W. Scherer, Sol Gel Science 1990 [67] L.E.Scriven, Better Ceramics Through Chemistry III . [68] gel dip J. Phys. III vol. 4, no. 7, pp. 1231 1242, 1994. [69] J. Non. Cryst. Solids vol. 82, no. 1 3, pp. 366 372, 1986.

PAGE 105

105 [70] 2nd edition Gelest product handbook, A survey of properties and chemistry, Hydrophobicity, Hydrophilicity and Silane Surface Modification . [71] M. Kirihara, Y. Asai, S. Ogaw Synthesis (Stuttg). no. 21, pp. 3286 3289, 2007. [72] l Brazilian Journal of Medical and Biological Research vol. 42, no. 4. pp. 305 311, 2009.

PAGE 106

106 BIOGRAPHICAL SKETCH Yung Chieh was born in Kaohsiung C ity, Taiwan. He obtained his B ache lor of Material Science and E ngineering from National Cheng Kung University (NCKU) in Tainan City, Taiwan. He attended the University of Florida starting in August 2012 in a m aster program and transferred to the doctorate program on May 2013 by Dr. Wolf gang Sigmund. During the time of pursuing his PhD he has applied 8 patents about development of durable superhydrophobic coating.