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Surface Modification of Silicon-Based Materials to Improve Antifouling and Fouling Release Properties

Permanent Link: http://ufdc.ufl.edu/UFE0043713/00001

Material Information

Title: Surface Modification of Silicon-Based Materials to Improve Antifouling and Fouling Release Properties
Physical Description: 1 online resource (137 p.)
Language: english
Creator: Chen, Jiun-Jeng
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: acrylates -- antifouling -- fouling-release -- silicone
Materials Science and Engineering -- Dissertations, Academic -- UF
Genre: Materials Science and Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Biofouling is the term that describes an accumulation of biological molecules, cells and organisms settling on an artificial surface1. Biofouling is a big challenge for the biomedical industry since biofilms form easily on surfaces such as door handle, surgical equipment, bed and many other medical devices, and could increase the chance of spreading disease in human's daily life. Biofouling is also challenging for shipping industry. The fouler accumulation on ship hull causes drag during navigation and thus, a ship loses fuel efficiency. The huge cost for periodical hull coating, cleaning, and hull corrosion repair due to biofouling draws great attention in shipping industry and U.S. Navy. This research is to develop chemically modified surfaces with antifouling properties. A novel method, which combines the thiol-ene chemistry and a classical sol-gel reaction was developed to graft acrylate-based copolymers onto glass and PDMSe surfaces. Low molar mass copolymers consisted of polyacrylic acid (PAA), polyacrylamide (PAAm), polymethyl acrylate (PMA), polyacrylamido-2-methyl-propanesulfonic acid (PAMPS) and PEG-functionalized acrylate polymers with selected PEG side chain lengths and degree of polymerization were synthesized in this study. The influence of surface chemistries and their combinations with engineered microtopographies on the deterrence of fouling cells, i.e., Ulva zoospores in the marine environment was investigated.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Jiun-Jeng Chen.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Brennan, Anthony B.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043713:00001

Permanent Link: http://ufdc.ufl.edu/UFE0043713/00001

Material Information

Title: Surface Modification of Silicon-Based Materials to Improve Antifouling and Fouling Release Properties
Physical Description: 1 online resource (137 p.)
Language: english
Creator: Chen, Jiun-Jeng
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2011

Subjects

Subjects / Keywords: acrylates -- antifouling -- fouling-release -- silicone
Materials Science and Engineering -- Dissertations, Academic -- UF
Genre: Materials Science and Engineering thesis, Ph.D.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Biofouling is the term that describes an accumulation of biological molecules, cells and organisms settling on an artificial surface1. Biofouling is a big challenge for the biomedical industry since biofilms form easily on surfaces such as door handle, surgical equipment, bed and many other medical devices, and could increase the chance of spreading disease in human's daily life. Biofouling is also challenging for shipping industry. The fouler accumulation on ship hull causes drag during navigation and thus, a ship loses fuel efficiency. The huge cost for periodical hull coating, cleaning, and hull corrosion repair due to biofouling draws great attention in shipping industry and U.S. Navy. This research is to develop chemically modified surfaces with antifouling properties. A novel method, which combines the thiol-ene chemistry and a classical sol-gel reaction was developed to graft acrylate-based copolymers onto glass and PDMSe surfaces. Low molar mass copolymers consisted of polyacrylic acid (PAA), polyacrylamide (PAAm), polymethyl acrylate (PMA), polyacrylamido-2-methyl-propanesulfonic acid (PAMPS) and PEG-functionalized acrylate polymers with selected PEG side chain lengths and degree of polymerization were synthesized in this study. The influence of surface chemistries and their combinations with engineered microtopographies on the deterrence of fouling cells, i.e., Ulva zoospores in the marine environment was investigated.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Jiun-Jeng Chen.
Thesis: Thesis (Ph.D.)--University of Florida, 2011.
Local: Adviser: Brennan, Anthony B.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2011
System ID: UFE0043713:00001


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1 SURFACE MODIFICATION OF SILICON BASED MATERIALS TO IMPROVE ANTIFOULING AND FOULING RELEASE PROPERTIES By JIUN JENG CHEN 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 201 1

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2 201 1 Jiun Jeng Chen

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3 To my wonderful wife, Shizuko Okusa

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4 ACKNOWLEDGMENTS I would like to express my sincere gratitude to my adv isor Dr. Anthony Brennan for the 4 year financial support and for his counsel at each milestone on the path of my graduation. I also want to thank his great consideration and support when I was facing the greatest depression in my life. I would also like t o thank Dr. Ronald Baney for teaching me a lot of silicone chemistry, and the other three of my doctoral committee members for my research assistance : Dr. Christopher Batich, Dr. Scott Perry and Dr. Stephen M iller I could not have completed this work wi thout the assistance of our precious collaborators: Dr. Maureen Callow, Dr. James Callow, and Dr. John Finlay. I must also thank g raduate students both past and present who have been helpful to my progress : Dr. Leslie Wilson, Dr. Christopher Long, Dr. Chelsea Magin, Dr. Dave Jack son, Dr. Julian Sheats Mr. Scott Cooper, Ms. Angel Eijiasi Mr. Sean Royston, Mr. Joe Decker, and Ms. Adwoa Baah Dwomoh. I would also like to thank the undergraduate Kimberly Struk who helped me on the research project. I also want to acknowledge those at the University of Florida that have assisted with instrumentation training and experimentation including Eric Lambers in the Major Analysis Instrumentation Center (MAIC) and Dr. Nathanael Stevens at the Particle Enginee ring Research Center (PERC). I also express my sincere appreciation for my parents and two older brothers, who continuously encourage me during my education. Finally, I would like to present my greatest gratitude to my lovely wife, Shizuko Okusa for her s pectacular spiritual support through the years of my PhD education in the United State, and for her efforts to give birth to our fine healthy and cutest baby, Jackson Okusa Chen during the last year of

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5 my PhD study. Jackson s coming has given me power to m ove myself to next milestone go graduating and finding a job.

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ .......... 10 LIST OF FIGURES ................................ ................................ ................................ ........ 12 LIST OF ABBREVIATIONS ................................ ................................ ........................... 14 ABSTRACT ................................ ................................ ................................ ................... 16 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 18 Scope of Research ................................ ................................ ................................ 18 Specific Aims ................................ ................................ ................................ .......... 19 Specific Aim 1 : Develop a method to graft acrylate based linear low molar mass homopolymers and copolymers on silicate surfaces using a combination of the thiol ene chemistry and surface coupling technique ....... 19 Specific Aim 2: Investigate the a ntifouling and fouling release efficiency of low molar mass a crylate based c opolymers against Ulva zoospores and Navicula diatoms ................................ ................................ ........................... 19 Specific Aim 3 : Identify if the chain architecture, tuned by the monomer side chain length and the molar mass of the PEGylated polymer brushes, plays a role in influencing the Ulva zoospores settlement and release. ........ 20 2 BACKGROUND ................................ ................................ ................................ ...... 22 Biofouling ................................ ................................ ................................ ................ 23 Marine Fouling Impact ................................ ................................ ...................... 23 Condit ioning Film Formation ................................ ................................ ............. 24 Factors Affecting Adhesion ................................ ................................ ............... 24 Surface energy / surface chemistry ................................ ............................ 25 Surface topography ................................ ................................ .................... 26 Mechanical property ................................ ................................ ................... 28 Surface Modification ................................ ................................ ............................... 29 Surface Modification Methods ................................ ................................ .......... 29 UV irradiation ................................ ................................ ............................. 30 Plasma ................................ ................................ ................................ ....... 30 Self assembled monolayers (SAMs) ................................ .......................... 31 Block copolymer adsorption ................................ ................................ ....... 31 Atom transfer radical polymerization (ATRP) ................................ ............. 31 Thiol ene reaction ................................ ................................ ...................... 32 Silani zation ................................ ................................ ................................ 32

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7 Types of Polymers ................................ ................................ ............................ 33 PEO based polymer ................................ ................................ ................... 33 Zwitterionic polymer ................................ ................................ ................... 35 Amphiphilic polymer ................................ ................................ ................... 35 Other polymers ................................ ................................ .......................... 37 Summary ................................ ................................ ................................ ................ 38 3 SURFACE MODIFICATION OF SILICATE GLASS USING 3 (MERCAPTOPROPYL)TRIMETHOXYSILANE FOR THIOL ENE POLYMERIZATION ................................ ................................ ................................ 41 Introduction ................................ ................................ ................................ ............. 41 Experimental Sec tion ................................ ................................ .............................. 43 Materials ................................ ................................ ................................ ........... 43 P rocedures ................................ ................................ ................................ ....... 44 Silanization ................................ ................................ ................................ 44 Grafting ................................ ................................ ................................ ...... 44 Surface Characterization ................................ ................................ .................. 45 Contact a ngle and s urface e nergy m easurement ................................ ...... 45 ATR FTIR ................................ ................................ ................................ ... 46 TM AFM ................................ ................................ ................................ ..... 46 XPS ................................ ................................ ................................ ............ 46 Gel p ermeation c hromatography (GPC) ................................ .................... 47 Ellipsometry ................................ ................................ ............................... 47 Results and Discussion ................................ ................................ ........................... 48 Contact Angle and Surface Energy ................................ ................................ .. 48 ATR FTIR ................................ ................................ ................................ ......... 49 TM AFM ................................ ................................ ................................ ........... 50 Molar Mass and Film Thickness ................................ ................................ ....... 50 XPS ................................ ................................ ................................ .................. 51 Conclusion ................................ ................................ ................................ .............. 54 4 ANTIFOULING AND FOULING RELEASE PROPERTIES OF ACRYLATE COPOLYMERS ON A GLASS AND ENGINEERRED MICROTOPOGRAPHIES ... 63 Introduct ory Remarks ................................ ................................ .............................. 63 Experimental Section ................................ ................................ .............................. 66 Material s ................................ ................................ ................................ ........... 66 P rocedures ................................ ................................ ................................ ....... 66 Synthesis of the MTS coupled g lass s lide (S MTS) ................................ ... 66 Graft of p oly(AA co AAm co MA co AMPS) onto the MTS coupled g lass s lide ................................ ................................ ............................... 67 Synthesis of the MTS coupled PDMSe s lide ................................ .............. 67 Graft of p oly(AA co AAm co MA co AMPS) onto the MTS coupled PDMSe s lide ................................ ................................ ........................... 68 Surface Characterization ................................ ................................ .................. 68 Contact a ngle and s urface e nergy m easurement ................................ ...... 68

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8 XPS ................................ ................................ ................................ ............ 70 TM AFM ................................ ................................ ................................ ..... 70 Mol ar mass d etermination of g rafted c opolymer on a g lass s lide ............... 70 Biofouling Assay s ................................ ................................ ............................. 71 Leaching t est ................................ ................................ .............................. 71 Settlement and r elease of Ulva z oospores ................................ ................ 71 Initial attachment and release of Navicula diatom ................................ ...... 72 Statistical methods ................................ ................................ ..................... 73 Results and Discussion ................................ ................................ ........................... 73 Chemical Composition of Modified Surfaces ................................ .................... 73 Contact Angle ................................ ................................ ................................ ... 75 Surface Energy ................................ ................................ ................................ 77 TM AFM ................................ ................................ ................................ ........... 79 Molar Mass ................................ ................................ ................................ ....... 79 Zoospore Settlemen t and Release on Copolymer grafted Glass Slides ........... 80 Zoospore Settlement and Release on Copolymer grafted PDMSe Slides ....... 81 Initial Attachment and Strength of Navicula diatom on Copolymer grafted PDMSe Slides ................................ ................................ ............................... 82 Summary ................................ ................................ ................................ ................ 83 5 PEGYLATED BRUSH AR CHETECTURE ON ANTIFOULING AND FOULING RELEASE AGAINST ULVA ZOOSPORES ................................ ............................. 95 Introduc tory Remarks ................................ ................................ .............................. 95 Experimental Section ................................ ................................ .............................. 97 Material s ................................ ................................ ................................ ........... 97 Synthesis of (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS) ................................ ............................. 97 Methods ................................ ................................ ................................ ............ 98 Coupling initiators onto a glass surface ................................ ..................... 98 ATRP g rafting ................................ ................................ ............................ 99 Surface c harac terization ................................ ................................ .......... 100 Mol ar mass d etermination of g rafted POEGMEMA ................................ .. 101 Ulva z oospore s ettlement and f ouling r elease a ssays ............................. 102 Results and Discussion ................................ ................................ ......................... 103 Contact Angle and Surface Energy ................................ ................................ 103 TM AFM ................................ ................................ ................................ ......... 104 XPS ................................ ................................ ................................ ................ 105 Film Thickness and Molar Mass ................................ ................................ ..... 105 Ulva Zoospores Settlement and Release Assay ................................ ............ 106 Discussion ................................ ................................ ................................ ............ 107 Summary ................................ ................................ ................................ .............. 110 6 CONCLUSIONS AND FUTURE W ORK ................................ ............................... 122 Conclusions ................................ ................................ ................................ .......... 122 Future Work ................................ ................................ ................................ .......... 124

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9 Acrylate Copolym ers Graft ................................ ................................ ............. 124 PEGylated Polymer Graft ................................ ................................ ............... 125 LIST OF REFERENCES ................................ ................................ ............................. 126 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 136

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10 LIST OF TABLES Table page 3 1 Surface treatment codes and descriptions ................................ ......................... 56 3 2 T he liqu L ) of WT, DM, GL and their corresponding L P L d ), Lifshitz L LW ), Lewis L + L ) and acid L AB ) .............................. 56 3 3 Sessile drop water contact angle of sample S MTS, S PAA, S PAAm, S PMA, S PAMPS and S P(AA AAm MA AMPS). Ten points were measured for each sample. The val ue expressed as averagestandard deviation. ............ 56 3 4 S S P S d ) val ues of polymer grafted samples calculated with the OWK method ............... 57 3 5 S ), Lifshitz S LW ), S + ), S ), and acid S AB ) parameters of S MTS and copolymer grafted samples calculated from LW AB method. ............................. 57 3 6 The number average mol ar mass (M n ), weight average mol ar mass (M w ), polydispersity (PD) and film thickness of polymer grafted samples ................... 58 3 7 XPS composition and high resolution data of S MTS and S P(AA AAm MA AMPS) ................................ ................................ ................................ ................ 58 3 8 C1s assignments in XPS analysis ................................ ................................ ...... 59 4 1 Initial solution and the final surface compositions of samples 3421, 3241, 3340, 3214, and 1423. ................................ ................................ ........................ 84 4 2 XPS composition and high resolution data of S MTS, sampl es 3421, 3241, 3340, 3214, and 1423. ................................ ................................ ........................ 84 4 3 Static sessile drop water (WT), diiodomethane (DM) and glycerol (GL) contact angles an d dynamic (advancing and receding) WT contact angles of S MTS and samples 3421, 3241, 3340, 3214, and 1423. Ten and five drops were measured on each sample for sessile drop and dynamic contact angle, respectively. The values are expressed as average stan dard deviation. ......... 85 4 4 L ) of WT, DM, GL and their corresponding L P ), dispersion L d ), Lifshitz L LW ), Lewis L + L ) and acid L AB ) ............................... 85 4 5 The surface ener S S P S d ) values of S MTS and copolymer grafted samples calculated with the OWK method. ................................ ................................ ................................ .............. 86

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11 4 6 S ), Lifshitz S LW S + ), S ), and acid S AB ) parameters of S MTS and copol ymer grafted surface s calculated from LW AB method. ............................. 86 4 7 The number average mol ar mass (M n ), weight average mol ar mass (M w ), and polydispersity (PD) of 3421, 3241, 3340, 3214, and 1423. ................................ 87 5 1 s ), polar, and dispersion S P S d ) values of POEGMEMA grafted surfaces calculated by Owens Wendt Kaelble method. WT: water; DM: diiodomethane ................................ ................................ ................................ ......................... 111 5 2 adv rec ), and adv rec ) of POEGMEMA grafted surfaces. ................................ 111 5 3 Measured subband binding energies and the theoretical ratios of grafted POEGMEMA 2080, POEGMEMA 950 and POEGMEMA 300. ........................ 111 5 4 The brush thicknesses, number average molecular weight (M n ), weight average molecular weight (M w ), and polydispersity (PD) of POEGMEMA grafted surfaces. ................................ ................................ ............................... 112

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12 LIST OF FIGURES Figure page 2 1 Schematic model with factors that influences marine biofouling ........................ 39 2 2 Schematic of A: sessile drop and B: captive air bubble contact angle measurements. ................................ ................................ ................................ ... 39 2 3 SEM images of Sharklet TM A) top down view. B), C) and D) are the side views with feature heights of 1 2 and 3 respectively .. ..................... 40 3 1 ATR FTIR spectra of S PAA, S PAAm, S PMA, S PAMPS and S P(AA AAm MA AMPS). Spectra were shifted vertically for better comparison. .................... 60 3 2 Three dimensional AFM images. A) acid cleaned slide. B) S MTS. C) S PAA. D) S PAAm. E) S PMA. F) S PAMPS. G) S P(AA AAm MA AMPS). .... 61 3 3 Curve fitting of high resolution scan of S MTS. A) C1s spectrum, peaks: 285.0eV and 286.8eV. B) S2p spectrum, peaks:163. 6eV and 167.4eV. ........... 62 3 4 Curve fitting of high resolution scan of S P(AA AAm MA AMPS). A) C1s spectrum, peaks: 285.2eV, 286.6eV an d 288.8eV. B) S2p spectrum, peaks:163.6eV and 167.7eV. ................................ ................................ ............. 62 4 1 ................................ ......... 87 4 2 Grafting copolymers onto a glass slide. A) hydrolysis of a glass slide. B) coupling of MTS. C) grafting acrylate based polymers. ................................ ..... 88 4 3 AFM typical images (amplitude mode). A) 3421. B) 3241. C) 3340. D) 3214. E) 1423. ................................ ................................ ................................ ... 89 4 4 The leaching test measured by UV using sample 3421 copolymer as the reference. ................................ ................................ ................................ ........... 90 4 5 Ulva zoospore assay on the copolymer grafted glass slides. A) Density of settled spores. B) The removal of spores. *= statistical different. ...................... 91 4 6 Density of settled spores on the standards and the five copolymer grafted surfaces plotted as a function of static water contact angle. ............................... 92 4 7 Density of settled spores on the copolymer grafted PDMSe slides (SM: smooth; SK: Sharklet TM ). *= statistical differ ent ................................ .................. 92 4 8 The initial attachment density of Navicula on the copolymer grafted PDMSe slides. *= statistical different groups. ................................ ................................ .. 93

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13 4 9 The removal of Navicula from the copolymer grafted PDMSe slides. *= statistical different groups. ................................ ................................ .................. 93 4 10 The remaining diatom attachment densit ies on the copolymer grafted PDMSe slides. *= statistical different groups. ................................ ..................... 94 5 1 Synthesis of A 10 Undecen 1 yl 2 bromo 2 methylpropionate and B. (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS) ..................... 113 5 2 1 H NMR of 10 Undecen 1 yl 2 bromo 2 methylpropionate. .............................. 114 5 3 1 H NMR of (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS) ................................ ................................ ................................ .......... 115 5 4 The appearance of Br in the XPS survey scan indicating the a successful coupling of BrPUTS onto a glass surface. ................................ ........................ 116 5 5 Receding contact angles ( rec ). A) POEGMEMA 2080 H. B) POEGMEMA 950 H. C) POEGMEMA 300 H. ................................ ................................ ....... 116 5 6 Three dimensional TM AFM images. A ) POEGMEMA 2080 H B ) POEGMEMA 2080 L C ) POEGMEMA 950 H D ) POEGMEMA 950 L E ) POEGMEMA 300 H F ) POEGMEMA 300 L. ................................ .................. 117 5 7 XP S C1s spectra with curve fittings of POEGMEMA 2080 L, 950 L and 300 L Peaks: A : O C=O (289.0 eV); B : C O (286.5 eV); C : C C/C H (285.0 eV). .. 118 5 8 Density of spores on PEG brush samples *= statistical different groups. ........ 119 5 9 The removal of Ulva spores from PEG brush samples. *= statistical different groups. ................................ ................................ ................................ ............. 119 5 10 Density of spores versus PEG side chain lengths (n=9, 19 and 45) on L series and H series POEGMEMA samples ................................ ...................... 120 5 11 Density of spores versus POEGMEMA brush thickness. ................................ 120 5 12 Density of spores versus POEGMEMA molar mass. ................................ ........ 121 5 13 Density of spores versus surface energies of POEGMEMA samples. .............. 121

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14 LIST OF ABBREVIATION S describes the risk of making a Type I error in statistical analysis AA Acrylic acid AA m Acryl amide AFM Atomic F orce M icroscopy AMPS A crylamido 2 methyl propanesulfonic acid ANOVA Analysis of Variance ATR FTIR Attenuated Total Reflectance Fourier Transform Infrared Spectrometry ATRP A tom T ransfer R adical P olymerization C. marina Cobetia marina DI Deionized water ERI Engineered R oughness I ndex HCl Hydrochloric acid LW AB Lifshitz van der Waals A cid B ase Method MA Methyl acrylate MTS 3 (Mercaptopropyl)trimethoxysilane Navicula Navicula incerta OWK Owens Wendt Kaelble m ethod p p value or observed signif icance level PAA Poly (acrylic acid) PAAm Poly (acrylamide) PAMPS Poly ( a crylamido 2 methyl propanesulfonic acid ) PDMSe Polydimethylsiloxane elastomer Silastic T2 Dow Corning Corporation PEG Poly(ethylene glycol)

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15 PMA Poly(methyl acrylate) RMS Root M ean S quare Re Reynolds N umber S AMs Self assembled M onolayers SEM Scanning E lectron M icroscopy SK Sharklet TM p attern TBT Tribulyltin (IUPAC name: Tributylstannane) TLC Thin L ayer C hromatography Ulva Ulva linza XPS X ray P hotoelectron S pectroscopy

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16 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy SURFACE MODIFICATION OF SILICON BASED MATERIALS TO IMPROVE ANTIFOULING AND FOULING RELEASE PROP ERTIES By JIUN JENG CHEN December 201 1 Chair: Anthony B. Brennan Major: Materials Science and Engineering Biofouling describes an undesirable accumulation of biological molecules, cells and organisms settling on a surface 1 B iofouling is challenging for the shipping industry and U.S. Navy. T he fouling accumulation on ship hull causes drag during navigation and thus, a ship loses fuel efficiency. The cost for the periodical hull coating and cleaning, and the repair due to the hull corrosion caused by marine biofouling, exceeds 600 million a ye ar for the shipping industry and U.S. Navy. 2 The motivation of this research is based upon a critical need for an effective marine antifouling and fouling release surface that is environme ntally neutral. This work is focused on modification of silicon based materials, i.e., the glass and poly(dimethylsiloxane) elastomer (PDMSe). A novel method, which combines the thiol ene chemistry and the surface coupling technique, was developed to graft acrylate based copolymers onto glass and PDMSe surfaces Low molar mass copolymers (5 8 kg/mol) consisted of p oly acrylic acid ( P AA) poly acrylamide ( P AAm), poly methyl acrylate ( P MA) poly acrylamid o 2 methyl propanesulfonic acid ( P AMPS) were synthesized with varied compositions. The copolymer grafted glass surfaces showed a

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17 92% reduction of Ulva zoospore attachment to the PDMSe standard. An enhanced fouling resistance to the Ulva zoospore (97% reduction to the PDMSe standard) was achieve d by combing this surface chemistry with the surface topography, i.e., Sharklet TM The antifouling and fouling release properties of the copolymer grafted PDMSe was also examined using another common marine organism, i.e., Navicula diatoms. The result indi cated an 87% reduction to the PDMSe standard on the initial diatoms cells attachment, and more than 60% removal after exposed to a low shear (26 MPa). This work also focused on the response of Ulva zoospores to the PEGylated polymer, i.e., poly(oligo ethy lene glycol) methyl ether methacrylate (POEGMEMA), with varied chain architectures tuned by the monomer side chain length and brush molar mass. The assay result indicated that the surfaces with longer POEGMEMA side chain lengths were more resistant to the zoospore settlement, but only weak correlations could be found between the fouling resistance and the brush molar mass.

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18 CHAPTER 1 INTRODUCTION Scope of Research Biofouling describes an accumulation of undesired bio logical organisms settling on a sur face. 1 Marine fouling is widely known to caus e a great economic impact for the shipping industry and n avies all over the world. Data shows that an effective antifouling coating may reduce fuel consumption by approximately $200 million for the U.S. Navy and $300 $400 million for U.S. commercial and pr ivate ships per year 2 Recently, there has been increased demand for non toxic marine coatings to combat energy shortages. 3 7 This work is focused on surface modification of the silicon based materials to improve marine antifouling and fouling release properties. A surface modification method was developed for graft of low molar mass copolymers with different chemical compositions. A series of low molar mass acrylate based copolymers were synthesized with tunable hydrophilic/hydrophobic balance and surface charges, and were evaluated fo r their antifouling properties against marine organisms, i.e., Ulva zoospores and Navicula diatoms. The influence of the combination of these low molar mass copolymers with the engineered microtopograph y, Sharklet TM on the attachment and release of marine fouling cells was also investigated. On the other hand, the effect of chain architectures of the polymer grafted surfaces on bioresponse of zoospores was of interest in this research Acrylate based PEGs were chose n in this study because of their well known antifouling properties against non specific proteins. The chain architecture was expressed in terms of PEG side chain length, brush molar mass, and film thickness. The atom transfer radical

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19 polymerization (ATRP) technique was utilized here in order to control the degree of polymerization (molar mass) with low polydispersities. Specific Aims Specific Aim 1: Develop a method to graft acrylate based linear low molar mass homopolymers and copolymers on silicate surf aces using a combination of the thiol ene chemistry and surface coupling technique Our previous study showed successful grafting of acrylate based copolymers to alumina particles in aqueous solution. 8 The objective of this aim is to graft the acrylate based homopolymers and copolymers from glass slides. The previous synthetic method was associated with thiol ene chemistry and ionic bonding between copolymers and particles. In this specific aim, it was hypothesized that an improved method to graft homopolymers and copolymers onto glass slides could be achieved by combing the thiol ene chemistry and the silane coupl ing technique. Completion of this aim is essential because this synthetic method allows for grafting of copolymers with a desired copolymer composition. Specific Aim 2: Investigate the a ntifouling and fouling release efficiency of low molar mass a crylate based c opolymers against Ulva z oospores and Navicula d iatoms Acrylate based materials have been long time used in the composition of antifouling paints 9 A mixture of acrylic acid (AA), acryl amide (AAm), and other unsaturated monomers with carboxylic or sulfonic acid functional groups in paint formulas have sh owed high antifouling ability with less than 10% fouled area on a tested board when dipped into sea water for 6 months 10 Copolymers composed of AA AAm methyl acrylate (MA) acrylamido 2 methyl propanesulfonic acid (AMPS) denoted as poly(AA co AAm co MA co AM PS) were grafted from the glass slide. It was hypothesized that the surface energies could be

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20 altered by adjusting the composition of each monomer. It was also hypothesized that an increased surface energy would show an increasing fouling resistance to the Ulva zoospores The acrylate copolymers with the same chemical compositions were also grafted to a smooth PDMSe and a topographical (Sharklet TM ) PDMSe to ev aluate their antifouling and fouling release properties against the Ulva zoospore s and Navicula diatom s. It was hypothesized that the dual effects will enhance the fouling resistance to both the Ulva zoospores and Navicula diatoms. All the bioassays were performed by Dr. Callow s group at the University of Birmingham, UK. Specific Aim 3 : Identify i f the chain architecture, tuned by the monomer side chain length and the molar mass of the PEGylated polymer brushes, plays a role in influencing the Ulva zoospores settlement and release. Surfaces coated with oligo ethylene glycol or poly(ethylene oxide ) (PE O ) or poly(ethylene glycol) (PEG) exhibit resistance to protein adsorption 11 13 The effect of PEG polymer chain arch itectures in terms of PEG side chain length, brush molar mass, and film thickness on Ulva zoospore settlement and release was not discussed yet. The architecture of the grafted PEG polymer, i.e., poly(oligo ethylene glycol) methyl ether methacrylate (POEGM EMA), was altered by the OEGMEMA monomers with selected OEG side chain lengths and the molar mass was controlled by the degree of polymerization. It was hypothesized that the attachment of Ulva zoospores would be lower on all POEGMEMA grafted surfaces tha n on PDMSe It was also hypothesized that the increased POEGMEMA side chain length and the POEGMEMA molar mass would increase the resistance to the Ulva zoospores settlement. I t was also hypothesized that, among the surface energies exhibited by different levels of POEGMEMA grafts, the

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21 increased surface energies would show an increasing antifouling against Ulva zoospores

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22 CHAPTER 2 BACKGROUND The development of antifouling coating has drawn great attention in recent years due to the increased demands in both biomedical applications and the marine environment 3 7 Biofouling describes an undesirable accumulation of biological molecules, cells and organisms settling on a surface 1 Biofouling is a big challenge for the biomedical industry since biofilms form easily on surfaces such as door handle, surgical equipment, bed and many other medical devices, and could increase the chance of spreading disease in humans. Data have shown that an estimated 1.7 million infections are caused from healthcare associated infections annually 14 B iofouling is also challenging for the shipping industry. The fouling accumulation on ship hull causes drag d uring navigation and thus, a ship loses fuel efficiency. In addition to the cost for periodical hull coating and cleaning, a huge expense on hull corrosion repair due to biofouling draws great attention in shipping industry and U.S. Navy. 2 The purpose of this research is to develop an antifouling surface by grafting low molar mass acrylate based copolymers with varied compositions. The main factors that will be manipulated are surface energ y/chemistry, and topography. The substrate can be modified with respect to designed combinations of the two factors to understand their relative importance on the biofouling problem. The Ulva zoospores was chosen as an ideal candidate for biofouling assay in this research due to, in addition to that it s a common marine fouler, its behavior of searching a surface and choosing a place to adhere. 15

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23 Biofouling Marine Fouling Impact It is widely known that marine fouling causes a great economic impact for the shipping industry and n avies all over the world. According to a research report 2 ships with hul l fouling may consume 40% more fuel than non fouling ones because the fouling causes a drag force on the ship resul ting in a decreased fuel efficiency In the past few years, the solution to reduce this economic impact was to coat a tributyltin (TBT) based paint onto ship hulls to reduce the biof ilm formation. In 2006, there were more than 70% ships in the world using 1 TBT coating saved shipping industries costs greatly in terms of decreasing fuel consumption and the frequency of dry docking and cleaning. 16 However, t he TBT d oes leach slowly into sea water and is harmful to mari ne ecosystems. Ther e is also a r isk that this chemical may indirectly influence the human food chain 17 Increasing concern about environment al impact caused by the use of TBT forced International Marine Organization ( IMO ) to hold an AFS(Anti fouling Systems on Ships ) convention in October, 2001, calling for an international ban of TBT use by January 1st, 2008 17 In 1985, the U.S. Navy estimated an amount of $130 million in annual savings on fuel consumption by using TBT contained coating 2 This number is based on 600 ships in fleet and a cost of $18 per barrel fuel. With the TBT ban in place, these costs jump even higher due to the high fuel cost today Data show s that an effective ant ifouling coating may save a fuel consumption of approximate ly $200 million for U.S. Navy and $300 $400 million for commercial and private ships per year for U.S alone 2 A ccording to the da ta from Naval Sea Systems Command ( NAVSEA ) 2008, a hull fouled ship causes a speed loss of approximately

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24 2% and increases fuel cost up to 45% depending on the size of the ship. Also, a n amount of $20 40 million is spent in under water hull coating and div er cleanings per year for U.S. Navy 18 A recent report showed that for just one mid si zed naval surface ship, i.e., DDG 51, the overall cost associated with hull fouling is $ 56 million per year or $ 1 billion over 15 years 19 Theref ore, now there is a need for development of environment ally benign coatings with high antifouling and foul release properties Conditioning Film Formation A co ndition ing film is generally composed of salts, proteins and carbohydrate compound. A substrate will start to acquire a conditioning film within seconds of exposure to an aqueous solution. A conditioning film is heterogeneous and its morphology is associated with the composition of t he adsorbed macromolecules. In most natural systems, the fouling matters will prefer contacting the previously formed conditioning film to the substrate. The following settlement of bacteria some other single cell species and their cell growth lead to an increased film thickness 7,20 Studies have sho wn that the conditioning film properties are affected by the substrate p roperties, and are correlated to the subsequent bacteria settlement. 1,21 This suggests that th e substrate surface chemistry directly or indirectly affects early conditioning film formation and influence the subsequent microscopic and macroscopic fouling. Factors Affecting Adhesion A biofouling adhesion m odel (Fi gure 2 1 ) has been proposed in Brenna n s group showing the factors affecting the adhesion of biological organisms. In this figure, the Ulva spore is chosen for probing the surface. The factors that affect the Ulva spores

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25 adhering to a surface include surface energy / surface chemistry, surface topography, and mechanical propert ies Surface e nergy / surface c hemistry Surface energy of a solid can be calculated from a series of contact angle measurements at equilibrium using solvents with different surface tensions. The contact angle is the angle created between ta ngent line of liquid/air interface and the solid s urface (Figure 2 2) Sessile drop and captive air bubble are two common methods used for contact angle measurements. Young s equation describes the interfacial energy relations of solid va por, solid liquid, and liquid vapor when the three phases reach equilibrium. At equilibrium, the chemical potentials of the three phases are equal. Young s equation is expressed as: SV = SL + LV cos (2 1) where SV SL and LV are the interfacial energy of solid vapor, solid liquid and liquid vapor, respectively. is the equilibrium contact angle. The Young s equation assumes a perfectly smooth surface. Surface roughness and surface contamination may cause a deviation in the equilibrium angle. When the liquid completely wets the solid surface, the equilibrium water contact angle is equal to zero. A surface with an equilibrium w ater contact angle less than 90 degree is called a hydrophilic surface while a surface with an equilibrium water contact angle greater than 90 degree is called a hydrophobic surface The surface energy of a material is determined based on measurement of co ntact angles using at least two probe liquids (polar and non polar).

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26 The broad interest of silicones used for marine biofouling control can be dated back to the research on surface energy in the 1970s 22 Baier et al. showed that the surface energy in the range of 20 25 mN/m correlates to the minimum cells attachment to a substrate. He noted that a substrate with a surface energy above or b elow this range would be termed bioadhesive range The surface energy ( 2 2 mN/m ) of the s ilicon e elastomer is in this range. Thus, it is extensively utilized for marine fouling research. Surface energy and surface chemistry are closely associated with each other since the surfa ce energy can be changed by grafting or adsorbing chemicals onto a surface. The surface energy change upon surfac e treatment is mainly determined by the exposed chemical specie itself, as well as chain orientations, molecular weight, and packing order. Fo r example, when a glass surface is grafted with OH terminated self assembled monolayers (SAMs), the surface energy increases, whereas CH 3 terminated SAMs tend to decrease the surface energy. Surface t opography In recent years the role of topography has been one of the focuses on study of bioa dhesion in our group. Sharklet TM a bioinspired engineered topography, was inspired by the spinner shark skin for its non fouling characteristic. The Sharklet TM topography (Figure2 3) produced from PDM Se has the featur es of 2 wide ribs with periodic lengths of 4 8 12 and 16 spaced 2 apart. This topography showed a 77% reduction in settlement of Ulva zoospores compare d with smooth PDMSe. 23

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27 Schumacher et al. int roduced an engineered roughness index (ERI) (equation 2 2), which is based on Wenzel s roughness (r), depressed surface fraction (1 S ) and the degree of freedom (df) of spore movement. 23 There is a linear correlation (R 2 =0 .69) of spore settlement densities versus ERI at a fixed feature spacing ( 2 m ) of ridges, pillars, triangles/pillars, and Sharklet TM on the topographical PDMSe. The topographies with highest ERI=9.5 ( Sharklet TM ) in this experiment showed a 77% reduction Ulva zoospores settlement compared to smooth PDMSe standard. (2 2) Schumacher et al also studied the effect of aspect ratio (feature height/feature width) of Sharklet TM engineered PDMSe on the settlement of Ulva zoospores 6 An increased aspect ratio resulted in an increase of fouling resistance for both Ulva zoospores and barnacle cyprids. They introduced the c oncept of nanoforce gradients, sug gest ing that the stress differen ce between two features (stress gradient) play ed a role on the settlement of marine organisms. 24 A predictable antifouling property model can be built upon engineering designed topographies. Recently, the ERI model was modified by replacing the degree of freedom (df) with the number of unique features (n). 25 The revised model, i.e., ERI II accurately predicted the attachment density of the zoospores on a range of topographies with better than 95% accuracy. Magin et al. 26 enhanced the model further by int roducing Reynolds number (Re) which took into account the size and the motility of the fouling organisms, i.e. ,Ulva zoospores and Cobetia marina bacterial cells. The attachment assay demonstrated that both organisms responded in a uniform manner to this ne w model.

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28 Mechanical p roperty Kendall s model describes the adhesion and surface energy of an elastic solid. 27 If we consider a hard cylindrical object contactin g with an infinite smooth plane surface of an elastic material, for which the thickness is much greater than the contact radius, then the critical stress necessary to remove the object can be expressed as: (2 2) w here E is the Young s modulus of the elastic material, is the interfacial surface energy a is the radius of the contact, and is Poisson s ratio of the sub strate. The interfacial surface energy is defined as the energy required for separation of the contacting surface from the substrate. If we consider the smooth substrate as a thin film and the radius of contact a is greater than the film thickness h then the critical stress becomes independent of a The equation could be shown as: 27 (2 3) In this equation, it assumes that the influence of time and strain on the bulk modulus of the thin film can be neglected. Recently, a few marine fouling adhesion studies were done associated with the fracture mechanical concept in the Kendall s model. Brady et al. reviewed eight different polymers used in fouling resistant c oatings. The fouling adhesion was indicated by the retention of cells on the surface. They demonstrated the fouling adhesion correlated well with (E ) 1/2 (R 2 = 0.89), which was better than with Young s modulus (R 2 = 0.82) or

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29 surface energy (R 2 = 0.75). 28 Another research studying the influence of elastic modulus on the release of the Ulva zoospores was examined on PDMS elastomer by Chaudhury et al.. 29 Different elastic moduli (0.2 9.4 MPa) were tuned by altering the cross link density of the PDMS n etwork. These PDMS networks with different moduli have the same film thickness. Data showed no significant increase in spore % removal as the modulus decreased from 9.4 MPa to 0.8 MPa but a distinct increase in % removal when the modulus further decreased to 0.2 MPa. Surface Modification Commercially available sil oxane elastomer surface s were modified by grafting to investigate their potential as anti fouling and fouling release coatings for marine applications. The intent is to increase the repulsive forces between the substrate and fouling molecules or organisms 4,11,30,31 PDMSe a s described above, wa s chosen for this research because it has a low surface energy (22 mN/m) low modulus (1 MPa) effective fouling release properties at low shear and it is considered non toxic However, the PDMSe does not perform well as an antifouling coating largely because protein adsorption occurs quickly 32 The re is an extensive body of literature focused on surface modification of PDMSe to improve its anti fouling performance 5,7,33 36 The next section of this dissertation is focused on the surface modification methods and polyme rs investigated for anti fouling and fouling release properties Surface Modification Methods S urface modification methods include UV irradiation 31,33,37 plasma treatment 38 40 self assembled monolayers (SAMs) 41,42 block copolymer adsorption 30 atom transfer radical polymerization (ATRP) 38,43 45 thiol ene reaction 8,46 49 and silanization 5,11,31,50

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30 E ach method was described briefly below. All of these methods are applicable to silicone s UV i rradiation Polymerization occurs at the surface by formation of radicals created by UV radiation. R adicals are formed by decomposition of a photoinitiator which transfers a radical to the substrate. The selection of a photoinitiator is important because it affects polymerization kinetics, polymerization efficiency, polymer molar mass, and polymer densit y. The surface modification of PDMSe by UV irradiation has been reported by Hu et al.. 33,51 The advantage of this technique is the one step process. The reaction time varies from several minutes to hours depending on the molar mass of the polymer synthesized. The drawback is that when a large area is used for grafting, an extra rotating device is required to ensure uniform polymer grafting. Uniform grafting is important because it would impact on the homogeneity of the grafted surface and thus the performance of coatings 51 Plasma Plasma is a state of matter composed of positive and negative charged particles generated by ionization of a gas. The radicals created in a plasma activ ate polymer surface s, such as PDMSe allowing for l inkage with chemicals, such as coupling agent s monomers or polymers. 40 The advantages of this technique, similar to the UV technique, are simple handling and fast reaction s Studies revealed that a plasma treatment of PDMSe leads to the surface oxidization to a depth of 100 160 nm. The oxidized surface is a brittle, microporous, and has a decreased organic moiet. 39,52 This transformation would expect an increase of the surface modulus, leading to changes of marine biofouling properties.

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31 Self assembled m onolayers (SAMs) The origin of SAMs date s back to 1946 when Bigelow et al. reported the adsorption of a surfactant to a metal surface to form a monolayer 53 This technique did not gain much attention until Nuzzo demonstrated the fabrication of n alkanethiolate SAMs on gold. 54 The method used the thiol to form a covalent bond with various transition metals, such as copper, silver, iron, platinum, and gold. Among these transition metals, the gold substrate is the most common used to form SAMs by or ganosulfur based materials, i.e. n alkanethiolate. The limitation of SAMs on gold however, is the high potential for oxidization of the thiol group. O xidization of the sulfur causes desorption of the chain when exposed to fluid flow 55 Therefore, the coating is unstable. B lock copolymer a dsorption B lock copolymer s are attached to surfaces by the physical adsorption of one segment. The other segment will extend from the surface. The attachment to a substrat e is based upon relatively weak Van der Waals bonds rather than covalent bonds. Triblock copolymers ( Pluronic TM ), i.e. poly(ethylene oxide) b poly(propylene oxide) b poly(ethylene oxide) or PEO PPO PEO, have been utilized lately to modify PDMSe using the hydrophobic PPO domain to quasi irreversibly adsorb onto the hydrophobic PDMSe surface 30,56 The weak Van der Waals bonds at the ad sorption interface ma d e the polymer desor b at low shear which makes it an unpromising for hull coating s 57 Atom transfer radical p olymerization (ATRP) Over the past decade, ATRP has become a popular technique because of the ability to control the mo lar mass and yield a low polydispersity of a synthesized

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32 polymer. 38,44,58 This surface modification techn ique involves immobilization of a surface initiator, such as haloester or chlorobenzyl compounds. The ATRP system requires a transition metal catalyst and its counterion which is able to form an ionic bond with metal s A number of metals, e.g., Ti, Mo, F e, Cu, have been shown to successfully mediate in ATRP. 59 Among all the metal complexes, the Cu complex is widely selected for its capability of being a catalyst with a wide range of monomers. 59 When ATRP is applied to a surface, t he propagation is carried out during the activation and deactivation of Cu I and Cu II complexes on the immobilized surface initiator. 60 This method needs a high purity nitrogen or argon environment to prevent the decay of catalyst efficiency caused by oxidization, and it usually takes several hours to attain high molar mass 44,61 Thiol ene r eaction The versatility of the t hiol ene reaction is evid ent in reports of oligomer and dendrimer synthesis 8,46 polymer functionalization 46 and polymer network formation 47 49 The mechanism involves radical addition of a thiol group to a vinyl group. Polymer chains grow from the sulfenyl radical, and vi a radical transfer to chains by hydrogen abstraction from another thiol group, creating a new sulfenyl radical. Polymers were synthesized when these propagation and chain transfer steps occur repeatedly I hypothesized that s urface modification could be ac hieved b y combining this technique with surface coupling chemistry, i.e., silanization. Silanization Silanization is a method to transform mineral component like silicate glass into an organofunctional material by using silane coupling agent. The origin o f coupling agent dates back to 1940s when glass fibers were used as reinforcement in organic resin

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33 composites. The debonding of resin from glass fiber occurred with water intrusion because the dissimilar nature of an organic compound and an inorganic miner al did not allow a formation of strong bonds, i.e. covalent bonds at the interface. The solution to this problem was studied and developed in late 1940s by introducing organofunctional silanes, or silane coupling agent as an intermediate material. 62 Coupling agents containing functional groups such as alkoxysilane or chlorosilane will react with silanol (Si OH) groups on glass or hydrolyzed PDMSe to form strong covalent bonds. The coupling agent also contain s organo functional groups that allows for further reaction with other chemicals, such as monome rs. In this dissertation, a combination of silanization and thio ene chemistry for surface modification will be addressed in Chapter 3 and Chapter 4. The other combination of silanization and ATRP will be addressed in Chapter 5. Both methods were allowed t o synthesize tunable and well defined polymer or oligomer grafted surfaces. Types of Polymers PEO b ased p olymer Poly(eth ylene oxide) (PEO) is a hydrophilic and thermoplastic polymer. This polymer has a unique repeating unit CH 2 CH 2 O and is commercially available in wide range of molar masses. Generally, poly(ethylene glycol) (PEG) refers to PEO with molar mass less than 10 kg/mol. PEG functionalized polymers are most widely used for its advantages of non toxicity, biocompatibility with living cells, and reducing the adhesion of proteins, cells and bacteria 36 A number of theoretical considerations suggested that the great entropic repulsion between hydrated PEO surface and protein is the main reason for the protein resistant phenomenon. 63 The entropic repulsion is due to the rapid movement of hydrated chains.

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34 This viewpoint is confluent with the perspective brought up by McPherson et al. 64 who believed that the protein adsorption prevention is due to the steric effect which PEO segments block the adsorption sites of the surface They showed that the surface graft density of PEO is more important than either PEO chain length or the molar mass of the grafted polymer for prevention of protein adsorption to Pluronic triblock copolymer (PEO PPO PEO) modified surfaces PEG based materials have also been shown to inhibit protein adsorption Fan et al. grafted polymer brushes of meth yl acrylate with PEG of various lengths, e.g., 4, 9, and 23 EG repeat units. onto Ti surfaces 43 T he fouling resistance to 3T3 fibroblast cell adhesion lasted three weeks with the longe st P EG side chains imparting the highe st showe d that PEG grafted onto the surface of poly(methyl methacrylate) ( PMMA ) film s was highly resistant to marine compounds i.e., proteins and phospholipid s 37 T he fouling resistance increased with concentration of PEG and number of EG units The antifouling effectiveness of short chain PEG (Mn= 250 g/mol) SAMs against marine organisms, i.e., Ulva zoospores and Navicula diatom was studied by Schilp et al through variations in end group chemistry i.e., hydroxyl ( OH), methoxy ( OMe),ethoxy ( OEt), propoxy ( OPr). 13 The most efficient antifouling performance was achieved using the hydroxyl terminated PEG and the least using the propoxy terminated PEG. The fouling resi stance positively correlated with the surface wettability i.e., water sessile drop contact angle The copolymerization of oligo EG methyl methacrylate and hydroxyl ethyl methacrylate were also show n effective at antifouling o f both Ulva zoospores (92% red uction) and Navicula diatom (85% reduction). 30

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35 Zwitterionic p olymer A z witterionic polymer has a feature of carrying both cationic and anionic charges in the structure, but is net charge neutral. An example of z witterionic polymer is poly(sulfobetaine methacrylate), which contains both a quaternary ammonium ( N + (CH 3 ) ) and a sulfate ( SO 3 ) functionality in the structure. These materials reportedly have good chemical stability and low cost, are commercial available and exhibit effective anti fouling ag ainst marine organisms and proteins, cells of interest for biomedical applications 65,66 Surface coatings with zwitterionic polymers, such as poly(sulfobetaine methacrylate) (polySBMA) and poly(carboxybetaine methacrylate) (polyCBMA) exh ibited resistance to non specific proteins and cell adhesion. 67,68 A study showed that a polyCBMA grafted glass surface performed 9 6 % reduction of fibrinogen protein compared to untreated glass surfaces. 69 Zhang et al. have also reported polySBMA grafted surface reduced settlement of Ulva zoospores by 92% and Navicula diatoms by 85% relative to glass slide s 65 66% of the attached zoospores were removed from these surfaces by an application of 63 KPa shear force, which demonstrated the surfaces are also effective at fouling release. The antifoul ing performance of zwitterionic polymers is attributed to strong surface hydration. This strong surface hydration, which is different from hydrogen bonding type materials e.g., PEG or PEO, is formed by electrostatically induced bond s to water. 66 This strong hydration layer prevents bioadhesives from forming interfacial bonds with the sur face. Amphiphilic p olymer An a mphiphilic polymer has both hydrophilic and hydrophobic functiona lities in the structure. It is generally in the form of a block copolymer. The hydrophobic segments,

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36 i.e., fluorinated polymer, are non polar, and have low surface energies, which reduce the formation of hydrogen bonds to bioadhesives secreted by marine or ganisms. The hydrophilic segments, i.e., PEO or PEG contain polar functionalities, which are known for protein repellency. The general goal of amphiphilic coating is to create a dynamic and chemica l l y complex structure that minimizes fouling and reduce s th e interfacial bonding strength Wooley s and Orber s research groups focus primarily on amphiphilic polymers for marine antifouling and fouling release Wooley s group synthesized amphiphilic coatings based on fluor inated and PEG ylated hyperbranched polymer s 4 The copolymer with a 55% PEG was the most efficient antifouling surface against Ulva zoospore attachment (86% reduction relative to glass). The least effective was the copolymer with 14% PEG, which reduced att achment by 75% relative to glass. Ober s group created the polystyrene block copolymers which have a linear structure rather than hyperbranched networks. 45 They synthesized a comb like block copolymer with PEG and fluoroalkyl ( CF 2 CF 2 ) in the pendant side chains These amphiphilic coatings had relatively high spore settlement, but significantly higher removal of both zoospores and diatoms than PDMSe. The authors attributed the high removal to the dynamic surface, on which the PEG and the fluoroalkyl chains would undergo surface rearrangement while the environment changes, i.e., applying a shear force by a water jet. The bonding strength of zoospores was weak on hydrophobic segments of the amphiphilic copolymer. 70 Therefore, the spores would likely be removed under the application of a low shear water flow.

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37 Other p olymers In addition to the mentioned three main categories of polymers used for current marine biofouling research, quaternary ammonium functionalized materials, organic inorganic nanohybrids, and superhydrophobic coating have been investigated. Majumdar et al. combine d th e fouling release properties of the PDMS and biocidal properties of the quaternary ammonium molecules to synthesize copolymer networks. 71 The PDMSe networks with quaternary ammonium molecules of various alkyl chain lengths (C1, C14 and C18) were studied. There was no trend between the ammonium alkyl chain lengths and their antifouling property. However, a general trend could be found on their fouling release properties. The coatings with the longest alkyl chain lengths (C18) showed the most fouling release properties against Ulva sporelings and N. incerta diatoms. The author proposed that the surface roughness is a factor that contributes to the fouling release properties since the surface with longer alkyl quaternary ammonium chains showed higher roughness (C18 > C14 > C1) and higher fouling release properties. T he organic inorganic nanohybrids, i.e., organosilica based xerogel prepared by sol gel process have been investigated for their potential as antifouling surfaces 72,73 The xerogel coated films are reportedly inexpensive, robust and have uniform roughness. 74 A broad range of surface energies (23 55 mN/m) were generated by adjusting the stoichiometry of the silicon alkoxide precursors. 73 The zoospores assay showed that the spore attachment densities correlated with surface energy and wettability. The attachment density was inversely proportional to surface energies (R 2 =0.80) and inversely proportional to wettability, i.e, sessile drop water c ontact angle (R 2 =0.83). The Navicula diatom assay showed similar initial densities on all the surfaces;

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38 however, the removal i.e., fouling release, of Navicula diatom cells was increased on surfaces with higher surface energies (R 2 =0.74). Superhydrophobic surfaces, such as leaves of the lotus plant, generally have a water contact angle greater than 150 o and roll off angle of less than 10 o 74 Scardino et al. made superhydrophobic topographies in coatings by spraying a mixture of siloxane copolymers with altered compositions and fumed silica onto a glass plate. 75 A surface roughness range of 600 nm 1400 nm was achieved in three different coatings, i.e., SHC 1, SHC 2, and SHC 3 but only the coating of SHC 3 was strictly nano scale over the entire surface. The topography dimensions o f the other two coatings, SHC 1 and SHC 2 ranged from nano to the microscale The SHC 3 significantly deterred the settlement of zoospores by 83% compared to a glass slide. The au thor attributed this high antifouling property of SHC 3 to its high work of adhesion required for formation of solid/liquid phase from solid/vapor phase. The zoospores are unlikely to attach to the surface without the creation of the liquid/solid phase. Th is nano architectured roughness with superhydrophobic characteristic provided a clue for future study on the fouling resistance. Summary Biofouling is a major ecological issue for the marine environment The economic impact to US shipping industries and the US Navy exceeds 600 million a year. 2 New technologies are needed to solve this problem by developing effective antifouling and fouling release coatings, which are also environmenta l neutral. Surface modification provides a versatile way to manipulate a surface with tunable modulus, surface energies, and surface roughness by selection of appropriate synthetic methods and materials.

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39 Surface modification can be combined other technolog ies such as topography to control bioadhesion. Figure 2 1 Schematic model with factors that influences marine biofouling 76 Figure 2 2 Schematic o f A: sessile drop and B: captive air bubble contact angle measurements.

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40 F igure 2 3 SEM images of Sharklet TM A) top down view B), C ) and D) are the side views with feature heights of 1 2 and 3 respectively 6 (with permission from Biofouling).

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41 CHAPTER 3 SURFACE MODIFICATION OF SILICATE GLASS US ING 3 (MERCAPTOPROPYL)TRIM ETHOXYSILANE FOR THI OL ENE POLYMERIZATION Introduction The motivation of this research is based upon a critical need for an effective marine antifouling and foul ing release surface that is environmentally neutral. A pplications including antifouling coatings 4,45 drug delivery 77,78 and microfluidic analytical devices 51,79 employ surface modifications with polymer ic graft s t hat control the substrate environment i nteractions or substrate organism interactions 4,11,30,31 The goal is to design surfaces that are functionally appropriate, efficient to apply and environmentally compatible Drug delivery requirements may include s pecific binding capabilities and resorption capabilities, whereas antifouling coatings require repulsive capabilit ies and long term stabilities. Some of the more common surface modification methods include UV irradiation 31,37 self assembled monolayer s (SAMs) 41,42 silanization 11,31,50 block copolymer adsorption 30 and atom transfer r adical polymerization (ATRP) 38,43 45 The UV irradiation method requires a high energy UV lamp and a specialized equipment to ensure unif orm polymer graft density over large surface areas. The graft density does affect the performance of antifouling coatings and microfluidic devices 51 SAMs are a method to make polymer grafted monolayers. However, a complication is the oxidation of the thiol group in the alkyl chain when adsorbed to a gold or silver substrate. The Reprinted with permission from Chen J J, Struk KN, Brennan A. Surface Modification of Silicate Glass Using 3 (Mercaptopropyl)trimethoxysilane for Thiol Ene Polymerization. Langmuir (Just Accepted Manuscript). Copyright (2011 ) American Chemical Societ y.

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42 oxidization of sulfur chang es surface affinity and causes desorption when exposed to fluid flow 55 Block copolymer adsorption, e.g., PluronicTM triblock polymers composed of poly(ethylene oxide) b poly(propyl ene oxide) b poly(ethylene oxide) or PEO PPO PEO, uses the hydrophobic PPO domain to quasi irreversibly adsorb onto a hydrophobic surface 30 However, these surfaces are thermally un stable and can only sustain low shear force compared to covalently bonded surface s 57 Over the past decade, ATRP has become a popular technique because of the ability to control molecular weight and graft density 38,44,58 T his method involves an immobilization of surface initiator, such as haloester or chlorobenzyl compounds. The propagation is carried out during activation and deactivation of CuI and CuII complexes 60 The process needs high pur ity nitrogen or argon environment and several hours to attain high molar mass 44,61 S urface m o di fi cations generally target high mol ar mass and high density of polymeric grafts. Our goal is to graft low molar mass and lower density oligomers and polymers Thiol ene che mistry, however, enables synthesis of oligomers directly on surfaces by a low cost and efficient method. The versatility of thiol ene reaction is evident in reports of oligomer and dendrimer synthesis 8,46 polymer functionalization 46 and polymer network formation 47 49 The mechanism involves radical addition of a thiol group to a vinyl group. Polymer chains grow from the sulfenyl radical, and via radical transfer to chains by hydrogen abstraction from another thiol group, creating a new sulfenyl radical. Polymers were synthesized when these propagation and chain transfer steps occur repeatedly. By combining this technique with surface coupling chemistry, a variety of surface modification s could be achieved.

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43 There are numerous examples of antifoul ing technologies based upon polymeric grafts in the literature ranging from PEGylated copolymers, fluoro copolymers to amphiphilic copolymers 4,34,45,70 Along with a diverse chemist r y, there are many d ifferent methods employed, all of which have advantages and disadvantages. We have selected a method with three simple steps which are demonstrated effective for a glass surface. This method is inspired by our previous efforts to stabilize alumina aqueous dispers ions at high concentrations, i.e., >60% solids 8 We chose acrylate monomers with very similar reactivi ty ratios. We adjusted the hydrophilic/hydrophobic balance and charge density of the synthesized oligomers through the monomer feed ratio s. P otassium persulfate was used as an initiator and 2 mercaptoethanol was used for thiol ene reaction in the previous study W e used the same initiator in this current study, but chose 3 (mercaptopropyl)trimethoxysilane (MTS) to function as the surface coupling agent and the chain transfer agent in the thiol ene reaction. We report here on the successful modification of g lass surfaces with poly acrylic acid ( P AA), poly acrylamide ( P AAm), poly methyl acrylate ( P MA) poly acrylamido 2 methyl propanesulfonate ( P AMPS) and a random copolymer based upon the four monomers using a thiol ene polymerization Experimental Section Materia ls Microscope glass slides (76mm x 25mm x 1mm) hydrogen peroxide (50 wt % solution in H 2 O ) and hydrochloric a cid (12.1M) were purchased from Fisher. D iiodomethane (DM), glycerol (GL), 3 ( mercaptopropyl ) trimethoxysilane (MTS) acrylic acid (99 wt%) (AA), acryl amide (>99 wt%) (AAm), methyl acrylate (99 wt %) (MA), 2 a crylamido 2 methyl 1 propanesulfonic acid (99 wt%) (AMPS) and potassium persulfate

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44 (>99 wt%) were purchased from Aldrich. Nanopure deionized (DI) water (18 .1 cm) was produced in house P rocedures All the chemicals were used as received and handled according to safe practices identified on material s safety data sheets. All the reactions were carried out at ambient conditions (22 C ) in a fume hood except for the treatment with MTS. S ilaniza tion Microscope g lass slides were flame treat ed with a B unsen burner by passing each slide over the flame 4 times The slides were cool ed for 3 minutes at room temperature and then placed in a glass coplin jar containing an aqueous solution of hydrochloric acid (4.7N) and hydrogen peroxide (8.4N). The slides were sonicated (Bra n son 3210) in the jar for 1 hour. E ach slide was subsequently washed twice with 25 mL DI water The cleaned slides were stored in DI water before silanization with MTS. Each slide was dried with a stream of nitrogen for 10 seconds. MTS (0.5 m L ) was pipetted onto each slide, which was then heated for 30 minutes under vacuum at 1 0 0 C The slide s w ere then cooled and transferred to a clean coplin jar containing 60 mL toluene, which was sonicated for 30 minutes. The silylated slides were each rinsed with methanol (30 mL) and then stored in methanol at 4 C prior to grafting Grafting The silylated slide s w ere removed from methano l and dr ied with nitrogen. The slide s w ere then racked in a staining dish The slides were immersed in an aqueous solution containing 100 mmol monomer, 0.135 mmol potassium persulfate and 80 mL of DI water The mixture was polymerized at 60 C for 3 0 minutes in a water bath T he slide s w ere washed with stream of DI water ( 100 mL), dried with nitrogen and stored in

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45 capped centrifuge tube s An abbreviation code and detailed description of the various surface treatments are listed in Table 3 1 Surface Characterization C ontact a ngle and s urface e nergy m easurement The e quilibrium c ontact angle of a sessile drop ( 5 L ) was measured with a Rame Hart model 500 goniometer for each surface treatment The average contact angle was determined by measurement of ten drops. The Owens Wendt Kaelble (OWK) 80 and Lifshitz van der Waals acid base (LW AB) m ethods 81 were used to calculate surface energies. The contact angl es were measured using two polar liquids, i.e., water (WT) and glycerol (GL), and one non polar liquid, i.e., diiodomethane (DM). The corresponding surface tensions ( L ) are 72.8, 6 3.4 and 50.8 mN/m, respectively. In OWK method, the polar ( S P ) and dispe rsion ( S d ) components of the surface energies of gra fted slides were determined by E q. 3 1 and E q. 3 2. ( 3 1) ( 3 2) The paramet ers and refer to the total surface tension, dispersion and polar components of the probe liquid, re spectively. The surface energ y ( ) of a modified surface is the sum of polar ( ) and dispersion ( ) components of the solid. In LW AB method, t he total surface energy ( ) of a solid is contributed from the electromagnetic interactions betwe en liquid and solid ( base interactions ( ) The (Lewis acid parameter) and (Lewis base

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46 parameter) were calculated from the E q. 3 3 to E q. 3 5 based on contact angle measurements with three different test liquids (WT, GL and DM) ( 3 3) ( 3 4) ( 3 5) L ) of test l iquids and their c orresponding components, i.e., polar ( L P ), dispersion ( L d ), Lifshitz L LW L + ), Lewis base L ) and acid base L AB ) were listed in Table 3 2 for calculation. ATR FTIR The spectru m was collected on a Nicolet 20SX spectrometer using germanium crystal with 32 scans at a resolution of 4 cm 1 A background spectrum was run and subtracted from the collected spectrum of each sample. The spectrum was displayed using Nicolet Omnic software. TM AFM A TM AFM was utilized to anal yz e surface morphology and roughness. The data were recorded by VEECO Dimension 3100 equipped with a Nanoscope III controller under tapp ing mode using a silicon pyramidal tip (10nm in diameter). T he scan size was set at 2 m. The scan rate and spring constant w ere set at 1.0 Hz and 0.001 N/m, respectively. A value of RMS roughness was calculated from the roughness profile of the sca nned ar ea using the Nanoscope software 7.0 XPS XPS was used to analyze the chemical composition of S MTS and S P(AA AAm MA AMPS) The spectra were recorded using Perkin Elmer PHI 5100 ESCA system

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47 with a magnesium take off angle under high vacuum ( ~2x 10 9 Torr). Both survey scans (0 1100eV) and high resolution C1s and S2p spectra were performed to determine the element composition. Both analyses and curve fitting were performed on AguerScan 3.2 (RBD instru ment) Ge l p ermeation c hromatography (GPC) The molar mass of grafted homopolymers and S P(AA AAm MA AMPS) were measured by GPC. A grafted polymer was cleaved off a slid e by mixing the slide with 20 m L chlorotrimethylsilane and 5 m L DI water in a glass Petri dish an d gently flushing the slide surface for 10 minutes. The solution was collected, pre cipitated in acetone and dried in vacuum The molecular weight was determined with Waters 410 using HPLC grade water as an eluent or Waters GPC Model V2K using HPLC grade T HF as an eluent. Both analyses were calibrated using poly(ethylene oxide) or poly ( styrene ) standards with PDs<1.1 Ellipsometry A n ellipsometry (FILMetric F20) coupled with FILMeasure software was used to measure the film thickness es of the homopolymers and S P(AA AAm MA AMPS) grafted surfaces in a reflectance mode Each measurement was done after baseline correction using a silicon wafer of (100) orientation as a reference. A silicon wafer of (100) orientation which was grafted with either each different homopolymer or copolymer using the same grafting method describing above, was used for estimation of film thickness 82 The data from five spots of each sample were averaged and reported as mean standard deviation.

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48 Results and Discussion Contact A ngle and Surface Energy The MTS coupled slides were prepared by a two step method, i.e., first acid wash and second silanization. The effectiveness of cleaning step was verified by measuring the contact angl e 83 The contact angle of the cleaned slide was less than 5 which was consistent values published by Cras et al .. 84 The water contact angle of the S MTS was 68.4 1.7 ( T able 3 3 ). This value was in the range of 53 70 which was consistent with the literature 84 Sin ce the contact angle of MTS coupled surfaces increases with increasing coupling density 84 o ur res ult indicates the MTS coverage is close to the maximum density Four different homopolymers, S PAA, S PAAm, S PMA and S PAMPS, and a copolymer of S P(AA AAm MA AMPS), with an initial monomer concentration ratio of AA:AAm:MA:AMPS=58:21:6:15 were grafted onto S MTS. The contact angles (Table 3 3) confirmed presence of grafts. The S P AMPS exhibite d the lowest contact angle ( 3.7 0.4 ), which was attributed to the combination of the sulfonic ac id and the amide groups in the graft. Replacement of these groups by carboxylic acid and primary amines, i.e., S P AA and S PAAm, increased the contact angle s to 55.4 0 .9 and 45 2 0.8 respectively. The S MTS PMA sho wed the highest contact value 63 8 1.2 due to its lower affinity for water. The S P(AA AAm MA AMPS) had a contact angle of 38 9 2.1 which was lower than the values of S PAA, S PAAm, and S PMA, but much higher than the value of S PAMPS. The surface energy was determined according to the OWK method that two polar nonpolar pair s of liquids, i.e., water diiodomethane (WT DM) and glycerol

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49 diiodomethane (GL DM) were used. Two polar liquids and one nonpolar liquid, i.e., WT, GL, and DM were used to determine the S L W S + and S valu es for the grafted surfaces as defined by the LW AB method The S PAMPS homopolymer surface energy S ) (Table 3 4 ) had the highest value, i.e., 65.5 mJ/m 2 compared to S PMA which was the lowest (45.9 mJ/m 2 ) as determined by the OWK method. The trend in surface energy of the grafts increased from the S PMA to S PAA to S PAAm homopolymers to S P(AA AAm MA AMPS) copolymer whi ch was lower than the S PAMPS. The range of 45.9 mJ/m 2 to 65.5 mJ/m 2 reflected the increasing hydrophilicity due to the increased conc entration of polar groups in the grafts. The surface energies measu red by the LW AB method (Table 3 5 ) differed by 4.4% or less than the values of the OWK method. ATR FTIR ATR FTIR spectra (Fig ure 3 1) w ere used to elucidate the surface chemistry of polyme r grafts. The chemical structure of the S PAA was validated by the broad OH stretch ( 3000 to 3600 cm 1 ), C H stretch at 2900 cm 1 and C=O stretch at 1650 1750 cm 1 85 The broad amide stretch ( 3200 3500 cm 1 ) and shift in carbonyl stretch to 1665 cm 1 (carbonyl in amide group) we re consistent with the structure of the S PAAm 85 The strong carbonyl peak at 1730 cm 1 was the evidence of PMA grafted surface 85 T here were overlap regions in th e spectrum of S PAMPS due to the multiplicity of functional groups. The breadth of the a b sorbance peak 3100 3500 cm 1 was assigned to a combination of O H stretch and N H stretch 85 The carbonyl group at 1740 cm 1 was a single peak The spectrum of S P(AA AAm MA AMPS) which wa s a composite of the four monomers, exhibited a multiplet between 1650 1740 cm 1 for the carbonyl groups.

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50 TM AFM The roughness and morphology of the gra fted surfaces were evaluated using TM AFM The RMS roughness of the acid c leaned slide was 0.72 nm (Fig. 3 2 a). This value was in the range, i.e., 0.3 nm to 3 nm reported in the literature for various cleaning methods 86 The RMS roughness was increased to 2.11 nm (Fig. 3 2 b) by treatment with MTS. The large difference in rough ness indicated the MTS formed a multilayer structure rather than a monolayer, which would not significantly change the surface roughness of the cleaned slide 86 The calculated RMS roughness values of polymer grafted surfaces (Fig 3 2c to 3 2g ) ranged from 3.55 nm to 5.92 nm These values were approximately 2 to 3 times greater than that of the S MTS i.e., 2.11 nm This supported, along with the extensive washing, that the structures were grafted onto the S MTS surface. The gross morphology varied with the graft compositions, e.g., S PAA, S PAAm, S PMA and S PAMPS which w er e attributed to the compositions that ultimately control the specific molecular arrangement and the potential to bond to the surface of the slide T he S P(AA AAm MA AMPS) exhibited the large st RMS roughness (5.92 nm) in this study. The copolymer composit ion would most likely induce large phase segregation that would expand the chains further beyond the homo polymers to increase roughness. However, molar mass differences must also be considered. The morphology of each grafted surface was heterogeneous as op posed to a uniform smooth layer This was interpreted as variations in molar mass. Molar Mass and Film Thickness The molar mass of the grafts was measured after cleavage from the glass surfaces. The process was assumed to be innocuous with respect to the acrylate

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51 backbone structure. The number average molar mass (Mn) of cleaved homopolymers and copolymers ranged from about 5 .3 to 8 .4 k g/mol (Table 3 6) The S PMA had the highest polydispersity (PD), i.e., 1.6. We attributed the higher value to the l ower solub ility of the MA monomer with water which resulted in phase segregation during the polymerization process The radical terminated chains would have a higher propagation rate in high MA concentration region s compared to low MA concentration regions due to concentration fluctuations in the mixture The result would be large r chain length distribution s As discussed previously, t he molar mass impacts the morphology of the grafted surface, as well as the surface energy and modulus. These factors are known to influence bioadhesion to surface s by bacteria, proteins, and cells 12,45,65 Ultimately the chemical composition defines the surface structure and bioresponse to it The ellipsometric thicknesses ( Table 3 6) of S PAA, S PAAm, S PMA, S PAMPS, S P(AA AAm MA AMPS) were 213 nm, 2 4 2 nm, 2 8 2 nm, 2 7 2 nm, 2 6 2 nm, respectively. The thickness of S PMA and S PAMPS were slightly higher than the others, reflecting their higher molar masses. Studies showed that a changed reaction time and temperature would result in different conversion of a monomer, as well as a different grafted molecular weight and thickness 87 We carried out the grafting under a fixed reaction time and temperature. The similar values of grafted molar mass or thickness of all grafted surfaces suggested similar reactivity ratios of AA, AAm, MA and AMPS, which was in agreement with the literature report. 8 XPS The existence of a MTS multilayer was supported by analysis of the elemental composition (Table 3 7).

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52 The elemental analysis showed t he atomic ratio of carbon to sulfur (C/S) was 6.4 which was greater than the theoretical value of 3. The theoretical value was based on a monolayer of MTS in which all the methoxy groups reacted du ring silanization. We assume that the phys i sorbed or unreacted MTS was removed by the extensive washing after silanization. However, the high C/S ratio could be explained by unreacted methoxy groups and adventitious carbon contaminants. T he thermal treatme nt should have fully condensed the MTS multilayer, which would be expected to eliminate unreacted methoxy groups 50 The structure of the MTS multilayer and existence of unreacted methoxy was analyzed further by XPS. T he C1s and S2p binding energies for the S MTS are 285.0 eV and 163.6 eV (Fig. 3 3A and 3 3 B) The C1s peak was further resolved by peak fitting into two chemical states with binding energies of 285.0 eV (77.4%) and 286.8 eV (22.6%). The 285.0 eV binding energy was attributed to the sum of the following three structures: C C (285.0 eV) 43 C S (285.4 eV) 88 and C Si (284.8 eV) 89 The 286.8 eV peak was assigned to the C O bond of unreacted methoxy groups 90 In addition, the S2p was resolved in to two chemical states with values of 163.6 eV and 167.4 eV for the C S H group and oxidized sulfur respectively 42 The composition ratio of C S H to oxidized sulfur wa s 4.3 (81.1/18.9), which means there was roughly one oxidized sulfur group per four MTS chains. This result wa s reasonable since thiol s are known to oxidize with time. The XPS measure ments were made approximately 5 hours after sample preparation. These results along with AFM roughness values and atomic ratios were consistent with the literature and support the formation of a multilayer by the MTS on the glass slide 42

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53 The che mical composition, by XPS (Table 3 7) of S P(AA AAm MA AMPS) copolymer showed a nitrogen peak in a survey scan of a graft e d surface This was attributed to nitrogen atoms in both AAm and AMPS. The eight C1s subband binding energies (Table 3 8) assigned to S P(AA AAm MA AMPS) were not individually resolved, i.e., a single broad peak was detected in the C1 s high resolution spectrum (Fig. 3 4A ). However, this is expected due to both the small differences in the binding energies, i.e., less than 0.5 eV, and the low atomic weight fractions in the polymer grafts So to estimate the relative compositions of the grafts, we combined C1s binding energies and performed a peak fit analysis. For example, the C1s chemical states with binding energies 284.8 eV, 285.0 eV and 285.4 eV were fitted into a single value of 285.2 eV. The three binding energies 285.2 eV 286.6 eV and 288.8 eV used in our peak fitting represent the average of values grouped by chemical similarity and ave r age differences of less than 0.5 eV The primary C1s peak located at 285.2 eV was ascribed to the C C backbone of the copolymer The 286.6 e V peak was mainly attributed to the carbon atom s adjacent to the amide bond ( C CONH 2 and C N H C = O) in AAm and AMPS, a s well as the carbon atoms of the ester group (COO C H3) in MA. The fitt ed peak at 288.8 eV was a ttributed to carbonyl carbon (289.0 eV) in AA and MA and those in AAm and AMPS i.e., 288.0 eV. Thus, a ll the assigned binding energies were in our peak fitting routine. The S2p spectrum (Fig. 3 4B) of S P(AA AAm MA AMPS) showed peaks at 163.6 eV and 167.7 eV which is in agreement with the literature value for the S2p binding energy of PAMPS i.e., 167.8 eV 90 The S2p peak rat io of 163.6 eV to 167.4 ( or 167.7 ) eV exhibited a significant decrease from 4.3 (81.1/18.9) (S MTS) to 1.4 (58.3/41.7 ) for

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54 the grafted S P(AA AAm MA AMPS) The large change was attributed to consumption of the thiol by the grafting reaction on the S MTS We were unable to estimate the composition of each polymer in S P(AA AAm MA AMPS) by calculating the ratio of each element and its assoc iated chemical states According to literature 91 the sampling depth for a 45 take off angle would be approximately 7 nm. Since the grafts on the surface s are not necessarily continuous or dense, one would expect the elements in the substrate to contribute to the XPS spectrum T he S i2p and O1s signals in XPS spectra w ould be attributed to both grafted copolymer and the glass slide Thus, we were unable to separate the Si2p and O1s signals to calculate the composition of grafts. Furthermore, the C1s signals might include carbons associated with MTS in the multi layer silanized structure. Although the compositions could not be quantified by th e XPS analysis, a qualitative analysis of S P(AA AAm MA AMPS) compositions support ed the FTIR analysis. We have initiated efforts to quantify the S P(AA AAm MA AMPS) compositions on the MTS monolayer by manipulation of the synthetic methods. First, we plan to evaluate a vapor deposition method for the MTS. Monolayer formation is enhanced by using the more dilute system of a vapor, which also facilitates better control of the kinetics of the condensation reactions at the surface. We are also investigating methods to reduce the oxidation of the thiol functionality of the MTS. The contributions of the MTS to the compositional analysis of the grafts would be reduced signifi cantly by minimization of multilayer ing. Conclusion A thiol ene polymerization was used successful ly to graft to glass slide s by a simple 3 step syntheses The presence of the grafts was confirmed by ATR FTIR, AFM

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55 and XPS The surface energies were correla ted with structure for the four homopolymer compositions, i.e., PAA, PAAm, PMA PAMPS homopolymers and the copolymer S P(AA AAm MA AMPS) A m ultilayer structure of S MTS was confirmed by AFM and XPS which prevented a quantitative assessment of the polymer graft compositions This surface grafting via a thiol ene initiated polymerization, provides a facile, cost effective and simple alternative method. It should prove useful for technologies such as antifouling, microfludic s and drug delivery

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56 Table 3 1. Surface treatment code s and description s Table 3 2. T L ) of WT, DM, GL and their corresponding L P L d ), Lifshitz L LW ), Lewis L + L ) and acid L AB ) 80,81,92,93 Table 3 3. Sessile drop water contact angle of sample S MTS, S PAA, S PAAm, S PMA, S PAMPS and S P(AA AAm MA AMPS) Ten points were measured for each sample. The value expressed as averagestandard deviation.

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57 Table 3 4. The S ), polar and dispe rsion component s S P S d ) values of polymer grafted samples calculated with the OWK method Sample Liquid S P S d S pair (mJ/m 2 ) (mJ/m 2 ) (mJ/m 2 ) WT DM 15.4 39.3 54.7 S PAA GL DM 7.3 41.8 49.1 mean 11.3 40.5 51.9 WT DM 23.2 35.0 58.3 S PAAm GL DM 16.6 36.5 53.0 mean 19.9 35.7 55.6 WT DM 11.3 37.1 48.4 S PMA GL DM 2.8 40.6 43.4 mean 7.1 38.8 45.9 WT DM 40.6 33.8 74.4 S PAMPS GL DM 23.1 33.5 56.6 mean 31.9 33.7 65.5 WT DM 29.5 30.9 60.4 S P(AA AAm MA AMPS) GL DM 25.5 31.6 57.1 mean 27.5 31.3 58.7 Table 3 5. The surface energ y S ), Lifshitz S LW S + ), S ) and acid S AB ) parameters of S MTS and copolymer grafted samples calculated from LW AB method.

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58 Table 3 6 The number average mol ar mass (M n ), weight average mol ar mass (M w ), polydispersity (PD) and film thickness of polymer grafted samples Table 3 7 XPS composition and high resolution data of S MTS and S P(AA AAm MA AMPS)

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59 Table 3 8. C1s assignments in XPS analysis Assignment Binding Energy(eV) Reference C Si 284.8 89 C C C, C SO 3 285.0 43,90 C COOR C S 285.4 88 C CONH 2 286.3 94 COO C H 3 286.4 88 C NHC=O 286.6 94 C C ONH 2 288.0 94 C C OOR 289.0 88

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60 Fig ure 3 1. ATR FTIR spectra of S PAA, S PAAm, S PMA, S PAMPS and S P(AA AAm MA AMPS). Spectra were shifted vertically for better comparison.

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61 Fig ure 3 2 Three dimensional AFM images A) acid cleaned slide B ) S MTS C ) S PAA D ) S PAAm E ) S PMA F ) S PAMPS G ) S P(AA AAm MA AMPS).

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62 Fig ure 3 3 Curve fitting o f high resolution scan of S MTS A) C1s spectrum, peaks : 285.0eV and 286.8eV. B) S2p spectrum, peak s :163.6eV and 167.4eV. Fig ure 3 4 Curve fitting of high resolu tion scan of S P(AA AAm MA AMPS) A) C1s spectrum, peaks : 285.2eV, 286.6eV and 288.8eV B) S2p spectrum, peaks :163.6eV and 167.7eV

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63 CHAPTER 4 ANTIFOULING AND FOUL ING RELEASE PROPERTI ES OF ACRYLATE COPOLYMERS ON A GLAS S AND ENGINEERRED MI CROTOPOGRA PHIES Introduct ory Remarks Biofouling describes the accumul ation of biological organisms on a surface 1 S hips with hu ll fouling may consume up to 40% more fuel than non foul ed ship s because the fouling c reates a drag force along the ship s hull. 2 This problem has caused a great financial burden to the shipping industry and the U.S. Navy. The U.S. Navy alone spends about one billion dollars a year cleaning up fouled ships 95 Data have show n t hat an effective antifouling coating may reduce fuel consumption by approximately $200 million for the U.S. Navy and $300 $400 million for U.S. commercial and private ships per year 2 Recently, there has been increased demand for non toxic and antifouling marine coatings to combat energy shortages 3 7 such as bacteria, microalgae, and diatoms tubeworms 1 The fo rmation of a biofilm starts with the formation of a condition ing film, which is composed of proteins and carbohydrate compound s Then, the settlement and growth of bacteria or other single cell species, lead to an increased film thickness 7,20 Ulva is a gr een alga commonly found on submerged structures. The Ulva plant produces motile spores which colonize surrounding surfaces 70 Many studies have indicated that the Ulva spore s prefer to settle on a hydrophobic surface rather than a hydrophilic surface 34,7 0 T he adhesion strength however is higher on a hydrophilic surface 96,97 Due to the specific spore behavior upon settlement and release, amphiphilic surfaces have been popul arly proposed as potential coatings for antifouling and foul ing release applications 4,45,70 Krishnan et al. synthesized a comb l ike block

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64 copolymer with PEG and fluoroalkyl ( CF 2 CF 2 ) in the pendant side chains These amphiphilic coatings had relatively high spore settlement, but significantly higher removal of zoospores than PDMSe. They hypothesized that the amphiphilic surface would undergo surf ace reconstruction upon expos ure to various surroundings An attempt to understand the zoospore behavior on the ambiguous surface, which contained both hydrophilic and hydrophobic regions was made by Callow 70 They d e signed a series of coatings with altered dimensions of PEGylated and fluorinated polymers on the same surface for spore settlement and release assay s The y showed that Ulva spores tend to settle on fluorinated region s, but become to settle less on the flu orinated regions if the region width decreased to 5 and less with the PEG background. In addition to the chemical treatment many efforts have focused on physical tuning of the surface. In recent years the role of topography has been one of the focuses on study of bioadhe sion in our group. Sharklet TM a bioinspired engineered topography, was inspired by the skin of a fast moving spinner shark for its non fouling characteristic. The Sharklet TM topography produced from PDMSe has features of 2 space topograp hy showed a 77% reduction in settlement of Ulva zoospores compared to smooth PDMSe 23 It was suggested that the topography of poly(dimethyl siloxane) elastomer (PDMSe) could be designed for antifouling based on the critical dimensions of marine organisms, such as Ulva zoospore 6,23 Acrylate bas ed materials have been used in antifouling paints for a long time 9 A mixture of acrylic acid ( AA ) acrylamide ( AAm ), and other unsatu rated monomers with

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65 carboxylic or sulfonic acid functional grou ps in paint formulas have show n high antifouling pro perty with less than 10% fouled area on a tested board when dipped into sea water for 6 months 10 I t is intriguing to examine acrylate coated surfaces for antifouling s ince these acrylate monomers in paints showed antifouling abilities,. A poly(dimethylsiloxane) elastomer (PDMSe) is a non toxic material used in marine fouling release application. PDMSe exhibits foul ing release ability due to its low surface energy ( ~ 23mN/m) and low modulus ( ~ 1MPa). However PDMSe has li mitations during surface characterization. The grafted polymer chains on a PDMSe surface tend to bury into the bulk and make them di fficult to be characterized by F ourier transform infrared spectroscopy (ATR FTIR) an d atomic force microscopy (AFM) because the PDMSe has low glass transition temperature ( 120 C). The other drawback is that there is always a little amount of unreacted siloxane molecules in the bulk after thermal curing 57 These small molecules may evaporate under high vacuum condition and contaminate an analytical device, i.e., x ray photoelectron spectroscopy (XPS). Due to these disadvantages, a silicate glass was chosen as a substrate in this study for its less characterization limitations and its similar chemical reaction mechanisms with PDMSe. In this paper, we propose a series of copolymers consisting of AA, AAm, methyl acrylate (MA) and acrylam ido 2 methyl propanesulfon ic acid (AMPS). PAA is hyd rophilic and possesses negative ly charged carboxylate groups. PAAm is also hydrophilic and it has lar ge hydrodynamic volume in water 8 PMA is less hydrophilic an d capable of forming a less hydrophilic domain when copolymerized with other hydrophilic polymers. PAMPS is extremely hydrophilic with the sulfonic acid functionality. A series of AA, AAm, MA and AMPS copolymers were prepared b y tuni ng

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66 the ratios of each monomer The surface wetting behavior and surface energies were va ried by the copolymer compositions. Two copolymer compositions were chosen to combine with mirco topographical PDMSe surfaces, Sharklet TM to achieve the optimal antifouling and fouling release properties. The antifouling and fouling release assays were tested against two common marine fouling organisms, Ulva zoospores and Navicula diatoms. Experimental Section Materials Microscope glass slides (76mm x 25mm x 1mm) hydrogen peroxide (50 wt % solution in H 2 O ), potassium persulfate (>99 wt%) chlorotri methylsilane diiodomethane, ethanol, methanol, toluene and hydrochloric a cid (12.1M) were purchased from Fisher. Silastic T 2 resin and curing agent were purchased from Dow Corning Corporation. Hexamethyldisilazane a llyltrimethoxysilane 3 ( mercaptopropyl ) trimethoxysilane (MTS) acrylic acid (99 wt%) (AA), acryl amide (>99 wt%) (AAm), methyl acrylate (99 wt %) (MA), 2 a crylamido 2 methyl 1 propanesulfonic acid (99 wt %) (AMPS) glycerol, glacial acetic acid and s odium hydroxide pellets were purc hased from Aldrich. Nanopure deionized (DI) water with resistivity greater than 18 M cm was produced in house. P rocedures Synthesis of the MTS coupled g lass s lide (S MTS) Microscope glass slides were rinsed with ethanol, flame treated with a Bunsen burner 3 4 times, let cool, and placed in a glass coplin jar. An acid peroxide solution with [HCl]= 4.7N and [H 2 O 2 ]=8.4N was prepared and transferred to the jar. The reaction was carried out in a sonicator (Brason 3210) for one hour. The slides were washe d with approximately 50 mL DI water and stored in DI water before silanization. A 5% (v/v)

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67 MTS/toluene solution was prepared and added to a staining dish with the dried slides in the slide rack. The solution reacted with the slides for two hours. The slide s were rinsed with approximately 10 mL toluene and 10 mL methanol, dried, and then cured in a 100 0 C vacuum oven for 30 minutes. Slides were rinsed again with methanol and stored in centrifuge tube s with methanol at 4 C prior to grafting. Graft of p oly(AA co AAm co MA co AMPS) onto the MTS coupled g lass s lid e An aqueous monomer solution was prepared using 200 mmol total of AA, AAm, MA and AMPS; 0.27 mmol potassium persulfate and 160 mL DI water. Due to the acidic character of AA and AMPS, an equmolar amoun t of s odium hydroxide was added to neutralize the solution. The solution was transferred into a staining dish with slides in the rack and the reaction was carried out in a 60 0 C water bath for 30 minutes. T he slides were then washed with copious amounts of DI water, blown dry with N 2 gas and stored in new centrifuge tubes with DI water for at least 24 hours to allow unbo u nd polymers to leach. Synthesis of the MTS coupled PDMSe s lide Silicon wafer mold fabrication and both smooth and micro topographical polydimethyl siloxane elastomer (PDMSe) slide preparation have been described in detail previously 24,98 Th e engineered microtopography ( ) used in this research wa s a pattern of repeating rectangles with 2 m feature width a nd spacing This microtopographical PDMSe surface replicated from a silicon wafer is shown in Figure 4 1. PDMSe slides (smooth and Sharklet TM ) were rinsed with ethanol and blown dry with a stream of N 2 An acid peroxide solution with [HCl]= 4.7N and [H 2 O 2 ]= 8.4N was prepared and transferred to the jar. The reaction was carried out in a sonicator (Brason

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68 3210) for 45 minutes. The PDMSe slides were washed with approximately 50 mL DI water and stored in DI water before silanization. A proper amount of glacial acetic acid was added to ethanol to adjust the pH to 4.5 5.5 before addition of MTS to make 5% (v/ v) MTS/ethanol solution. The solution was stirred for at least 10 minutes. Each PDMSe slide was dried with N 2 followed by transferring the MTS/ethanol solution to cover the slide liberally but not to allow solution to spill over to the back side of the sli des. Allow the MTS to react with PDMSe slide for 30 minutes under N 2 The PDMSe slides were then rinsed with ethanol, dried with N 2 and cured in a 100 C vacuum oven for 20 minutes. After cooled down in ambient (22 C) under vacuum, the MTS coupled PDMSe sl ides were immediately used for copolymer grafting. Graft of p oly(AA co AAm co MA co AMPS) onto the MTS coupled PDMSe s lid e The procedure of grafting p oly(AA co AAm co MA co AMPS) onto the MTS coupled PDMSe s lid e was the same as described in the section of G raft of Poly(AA co AAm co MA co AMPS) onto the MTS coupled Glass S lid e but use the PDMSe slide to substitute a glass slide. Surface Characterization Co ntact a ngle and s urface e nergy m easurement Sessile dr op water contact angle and dynamic contact angle were measured using a Rame Hart model 500 goniometer. The drop volume in sessile drop contact angle measurement was 5 Ten drops were placed on each surface and allowed to reach equilibrium prior to measu rement. For dynamic contact angle measurement s the advancing contact angle was measured by the maximum angle with a 3 while the receding contact angle was the minimum angle when

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69 the liquid was removed at 0.1 rements from the 3 Five spots were analyzed on each surface. B oth th e Owens Wendt Kaelble (OWK) approach 80 and Lifshitz van der Waals acid base (LW AB) m odel 81 were adopted for surface energy measurement using two polar liquids: DI water (WT) and glycerol (GL), and one non polar liquid, diiodomethane (DM), with the corres ponding surface tensions: L = 72.8, 64.0 and 50.8 mN/m. The polar ( S P ) and dispersion ( S d ) components of the surface energies of S MTS and copolymer grafted slides were determined by E q. 4 1 and E q. 4 2 80 ( 4 1) ( 4 2) The paramet ers of and refer to the total surface tension, dispersion and polar components of the probe liquid respectively The surface energies ( ) of the modified surfaces are the sum of polar ( ) and dispersion ( ) components of the solid. T he to tal surface energy ( ) of a solid is the sum of the electromagnetic interactions between the liquid and solid, termed as Lifshitz van der Waals ( ), and base interactions ( ), as shown in E q. 4 3 to 4 5. The (Lewis acid parameter) and (Lewis base parameter) are calculated from the three equations based on contact angle measurements with the three different test liquids mentioned above ( 4 3)

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70 ( 4 4) ( 4 5) XPS XPS was used to analyze the chemical composition of MTS coupled and copolymer grafted surfaces. The Perkin El ray source was performed to acquire both survey and multiplex (C1s and S2p) spectra. The samples were analyzed at 15 take off angle under high vacuum (~2x10 9 Torr). Both analyses and cur ve fitting were performed with A ug erScan 3.2 (RBD instru ment). The 10% Gaussian Lorentz ian band type was chosen for curve fitting in this paper. TM AFM A TM AFM was utilized to anal yz e surface morphology and roughness. The data were recorded by VEECO Dimension 3100 equipped with a Nanoscope III controller under tapping mode using a silicon pyramidal tip (10nm in diameter). T he scan size was set at 500 nm The scan rate and spring constan t w ere set at 1.0 Hz and 0.001 N/m, respectively. A value of RMS roughness was calculated from the roughness profile of the sca nned area using the Nanoscope software 7.0 Mol ar mass d etermination of g rafted c opolymer on a g lass s lide A copolymer grafted glass s lide was mixed with 20 mL chlorotrimethylsilane in a glass Petri dish. Then a volume of 5 mL DI water was added. The slide surface was gently flushed using a glass pipette for 10 minutes. The solution was collected and pre cipitated in acetone. The p for analysis.

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71 The molecular weight was measur ed on the Waters 410 coupled with Phenomenex columns (BioSep SEC s2000 and BioSep SEC s4000) using HPLC water as the eluent. The equipment was calibrate d with several low polydispersity poly(ethylene oxide) standards. Biofouling Assay s The settlement and release assay of Ulva zoospores, and the initial attachment and release assay of Navicula diatoms were performed at the University of Birmingham, UK by C s group. Leaching t est Samples were soaked in DI water for 24 hours at 2 2 0 C in a centrifuge tube The water in the tube was then examined by UV spectrophotometer to determine if copolymers were present. The copolymer 3421 was used as a standard. A calibration curve was created by testing the c opolymer 3421with gradient concentrations (10 ppm, 5 ppm and 1 ppm). Settlement and r elease of Ulva z oospores Six replicates of each co polymer grafted surface were prepared. The f lame treated glass slides and S ilastic T2 coated slides were as standards in this experiment. There were six replicates used in the Ulva spores settlement assay (3 replicates) and release assay (3 replicates) The assays were performed as described previously 97 Briefly s amples were immersed in the artificial sea water (ASW) (Instant Ocean ) for 2 hours before the assay. A 10 mL aliquot of spore solution ( 1.5 x 10 6 spores/m L ) was added into a Petri dish and incubated in the dark for 45 minutes at 20 0 C. The samples were gently rinsed with ASW to remove unattached spores and fixed with 2% glutaraldehyde in seawater for 10 minutes The number of spore s was count ed using an

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72 image process system connected to a fluorescence microscope. The mean spore densit y was determined based on 30 fields of view (0.15 mm 2 ) on each of the three slides. For release assays, a turbulent flow apparatus providing a shear stress of 50 MPa was applied to the other three unfixed slides The spores remaining on the slides were fi xed and counted. The remaining spore density was determined using the same method described above. Initial attachment and release of Navicula diatom The Navicula diatom assays were performed on the acrylated grafted PDMSe (smooth and Sharklet TM ). Six replicates of each surface were prepared Three replicates were used for the initial attachment assay while the other three were for the release assay. The details of the assay have been described elsewhere. 97 Briefly, the Navicula cells we re cultured in F/2 medium for 3 days to give a log phase growth. The cells were washed in the fresh medium 3 times, harvested and diluted to give a suspension with a chlorophyll a content of g / m L Cells were settled by gravity in each testing dish co ntaining 10 mL of suspension on the bench at ambient (~20 C) for 2 hours. Slides were exposed to a gentle submerged wash in seawater to remove unattached cells and were fixed in 2.5% glutarald ehyde The number of cells was count ed using an image process sy stem connected to a fluorescence microscope. The mean cell density was determined based on 30 fields of view (0.15 mm 2 ) on each of the three slides. The other three slides were exposed to a shear stress of 26 Pa in a water channel after initial attachment was established. Samples were fixed with 2.5% glutaraldehyde

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73 and dried by a stream of air. T he cell density was determined the same way as described above. Statistical m ethods The Ulva zoospore density and Navicula diatom density were reported as a mean nu mber of the spores or diatom cells per mm 2 from 30 counts on each of the three replicate slides (n=90) with 95% confidence interval. The Tukey method was used for multiple comparisons of all different surface treatments to evaluate their statistical differ ences. 99 Results and Discussion The sample code of each poly(AA co AAm co MA co AMPS ) grafted slide with initial monomers (AA, AAm, MA, AMPS) compositions before polymerization and the final surface compositio ns are listed in Table 4 1. The four digits of each sample code correspond to the initial mole ratio of AA, AAm, MA and AMPS. The determination of the final copolymer compositions will be discussed in the next paragraph The synthesis included three steps: hydrolysis of a glass slide, coupling MTS to the hydrolyzed glass slide and grafting copolymer via thiol ene reaction to the MTS coupled glass surface, as shown in Figure 4 2 A, B and C. Chemical Composition of Modified S urface s The XPS composition and high resolution data of the S MTS and five copolymer samples are listed in Table 4 2. T he C1s spectrum showed two distinct peaks at 285.1 eV (71.4%) and 286.8 eV (28.6%) on S MTS The 285.1 eV peak was attributed to C C (2 85.0 eV) 43 C S (285.4 eV ) 88 and C Si (284.8 eV) 89 The other peak, 286.8 eV, referred to C O bond from the unsil anized methoxy group. 90 T here was approximately one unsilanized methoxy group on each MTS molecule which was estimated by the

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74 ratio of the two peaks (71.4 : 28.6 = 3 : x; x=1.2). Also, the S2p spectrum of S MTS showed two peaks at 163.7 eV and 167.9 eV, which correspond ed to the thiol and oxidized sulfur groups, respectively. It is known that the thiol group is oxidized with time in the air 42 Our previous experimental data showed that approximately 1 9 % of the sulfur oxidized after exposed to the air for 5 hours at 25 0 C. We reduced the sulfur oxidization to 2.1% by shorten the preparation time for XPS measurement. All the MTS coupled slides were stored in methanol at 4 0 C no longer than 24 hours before further grafting. The polymer composition in each of the five copolymer samples was determined by both the element composition and high resolution data The calculation of the surface composition is discussed below using the sample 3421 as an instance. The S2p peaks with binding energies of 163.8 eV and 168.3 eV referred to the thiol group (S H) in MTS and both the sulfonate in PAMPS and oxidized s ulfur in MTS, respectively. 90 T he amount of the oxidized sulfur in MTS was subtracted from the total amount of sulfur generated from the 168.3 eV t o determine the amount of PAMPS in a sample, The amount of oxidized sulfur in MTS wa s estimated by the oxidized sulfur in sample 3340 (no PAMPS) which assumed that the MTS on the five samples had the same oxidization level This assumption was reasonable since all the copolymer grafted surfaces were synthesized using the same protocol T he relative low sulfur composition (0.3%) in the sample 3340 also revealed that the surface was fully covered by the grafted copolymers. The amount of PAMPS in sample 3421 was calculated to give a value of 0.43 [(1.4 x 37.4%) (0.3 x 29.7%)] The amount of PAA was determined by the sodium element.

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75 A stoichiometric amount of sodium hydroxide was added to the aqueous solution to neutralize the acidic solution from the AA and AMPS monomers prior to polymerization. Since there was no sodium detected in the S MTS, we could assume the total amount of sodium was from PAA and PAMPS. Therefore, the amount of PAA in the sample 3421 was 1.27 ( 1.7 0.43 ) The amount of PAAm was 1.57 which was obtained by subtracting the amount of PAMPS from total nitrogen ( 2.0 0.43 ) Finally, the amount of PMA was determined by the total amount of carbonyl groups from all four components. T he binding energ ies of the carbon on C=O were 288.0 eV for an amide group 94 and 288.6 e V for the carbon on an ester group 88,100 W e fitted both types of C=O into one peak ( 288.4 eV ) for two reasons Firstly, i t i s difficult to resolve two peaks with binding energy difference less than 0.6 eV. Secondly the surface charges usually occur on a substrate of low electrical conductivity during the XPS analysis, which causes a shift of the spectrum to a higher binding energy. An error of less than 0.3 eV i s usually inevitable after shift correction. T he amoun t of PMA was calculated to give a value of 0.6 ( 34.8 x 11.1% 1.27 1.57 0.43 ) The ratio of PAA : PAAm : PMA : PAMPS in sample 3421 was 1.27 : 1.57 : 0.6 : 0.43, which was normalized to 33 : 41 : 15 : 11. The same calculations and assumptions were app lied for the other four samples to determine their chemical compositions. Contact Angle The sessile drop contact angle measurement of a hydrolyzed glass slide showed an angle less than 5 which suggested a high concentration of hydroxyl groups on the glas s surface 83 The high hydroxyl concentration on the surface promoted the probability of MTS reaction with the glass surface during silanization. The contact angle

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76 mea surements of the MTS coupled glass slides were 62.6 2.0 (Table 4 3), which suggested high MTS coverage on the surface and was in agreement with the value reported by Cras group 84 The advancing and receding angles of the S MTS were 67.1 1.9 0 and 37.0 0.6 respectively. The advancing a ngle was in agreement with that reported by Schmid s group 101 however, the receding angle was 10 lower. This variation was most likely due to the different acid treatment and silanization conditions i.e., MTS concentration, reaction time and temperature, which influenced surface coverage and roughness. The copolymer grafted surfaces were also characterized by goniometer. The s tatic water contact angle values ( Table 4 3 ) of a ll the five samples exhibited signif icant differen ces ( =0.05) between any of two surfaces Th is result reflected the chemical composition differences of each grafted surface. The contact angles of the homopolymers used in the copolymer composition provided a clue to tell the ration ality of the contact angles between each copolymer grafted surface. In Chapter 3, the contact angles were reported 3.7 0.4 for PAMPS, 42.3 4.9 for PAA, 47.6 6.0 for PAAm, and 62.5 2.4 for PMA. PAMPS has both amido and sulfonate groups which are capable of forming hydrogen bond s and ionic bonds with water Both bonds lead the PAMPS to have the low est contact angle. PAA and PAAm have carboxylic acid groups and amide groups, respectively to form hydrogen bonds with water and thus exhibit medium con tact angle s PMA only has ester groups to bond with water, which reflects its less hydrophilic nature. The sessile drop contact angle s of the five copolymers yield a trend that correlates to the surface composition. The samples with higher MA composition, i.e., 3340 and

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77 3241, exhibited higher contact angle values o f 51.36.4 and 46.45.4 while the lowest contact angle was appeared on the sample 3214 (30.5 3.5 ), which had highest AMPS and lowest MA composition The dynamic contact angles (Table 4 3) of t he S MTS and the five copolymer samples were determined by sessile drop method using DI water as a test liquid. Among the five copolymer grafted surfaces 3340 had the highest advancing contact a a = 63.4 0.7 ) which reflected again its least hydrophilic nature among the five Contrary to 3340, 3214 had the lowest advancing contact a a = 38.0 2.0 ) because it contained more hydrophilic components in the composition. The same trend was observed for the receding contact angles ( r ) on the five surfaces The dynamic contact angle hysteres e s ( a r ) ( Table 4 3) of the five s urfaces range d 27.0 37 .0 The hystereses reflected the significance of surface reorganization. The surface reorganization is due to short r ange segment rotation s of each polymer components in the copolymer chain. The various levels of hydrophilicity of the components in the copolymers were a driving force for local chain rotations to reach an equilibrium state with the water/air interface. Surface Energy The surface energies along with the polar, dispersive, Lifshitz van der Waals and acid base interaction components of MTS couple d surface and copolymer grafted surfaces were determined by using Owens Wendt Kaelble (OWK, E q. 4 1, 4 2) and Lifshitz van der W aals acid base (LW AB, E q. 4 3 to 4 5) approaches. The surface energy was determined according to the OWK method that two polar nonpolar pair s of liquids, i.e., water diiodomethane (WT DM) and glycerol

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78 diiodomethane (GL DM) were used. T he LW AB model deve loped by van Oss et al. 81 further resolve d een electron acceptor and donor Two pol ar liquids and one nonpolar liquid, i.e., WT, GL, and DM were used to determine the S L W S + and S values for the grafted surfaces as defined by the LW AB method. Static sessile drop contact angles of each modified surface were measured in this study a nd were tabulated in Table 4 3 L ) of test l iquids and their corresponding components, such as polar ( L P ), dispersion ( L d ), Lifshitz L LW L + ), Lewis L ) and acid L AB ) are listed in Table 4 4 80,81,92,93 The calculated s S ), p olar and dispersion component s S P S d ) of S MTS and copolymer grafted s urface s by the OWK method are given in Table 4 5. The surface energy of S MTS was 48.3 mJ/m 2 which had relatively low polar component (13.6 mJ/m 2 ) compared to the five acrylate coated surfaces. Among the five co polymer grafted surfaces, 3340 h ad the lowest surface energy ( 53.1 mJ/m 2 ), while 3214 had the highest surface energy ( 62.6 mJ/m 2 ). Since the dispersive component of the five copolymer grafted surfaces were similar (31.1 35.4 mJ/m 2 ), the polar component played a significant role in the total surface energy. The polar component showed the highest for 3214 (29.9 mJ/m 2 ) and the lowest on 3340 (19.8 mJ/m 2 ), which ali gned with the AMPS concentration in these copolymers The surface energies of S MTS and copolymer grafted s urface s calculated using the LW AB method are listed in Table 4 6 and are similar to those obtained from the OWK method. The surface energies of the S MTS and samples 3421, 3241, 3340, 3214, and 1423 were 49.1, 60.4, 57.6, 54.4, 62.1 and 59.3 mJ/m 2 respectively, while

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79 those determined by OWK method were 48.3, 60.8, 57.2, 53.1, 62.6 and 58.3 mJ/m 2 The relative differ ence of the values between both met hod s was less than 2.4%. For all five copolymer samples, the value of the Lewis base component S ) was higher than the Lewis acid component S + ) which indicates strong election donating characteristic. This characteristic was attributed to the oxygen atoms in carbonyl or acid groups and nitrogen atoms in amide groups. The Lewis base component S ) showed the highest for 3214 (30.4 mJ/m 2 ) and the lowest for 3340 (19.9 mJ/m 2 ), which was explained by the relative amounts of AMPS and MA in these copolymer s Since AA and AAm have surface energies between AMPS and MA, they are not expected to play a significant role in the copolymer surface energy. TM AFM The su rface roug hness and morphology of the grafted surfaces were evaluated using TM AFM The calculated RMS roughness values of polymer grafted surfaces (Fig 4 3a to 4 3e ) ranged from 4.42 nm to 5. 75 nm These values were close to those of homopolymers and the copolymer S P(AA AAm MA AMPS) with the composition of AA/AAm/MA/AMPS=58:21:6:15 reported in Chapter 3. The gross morphology varied with the graft compositions, e.g., 3421 3241 3340, 3214 and 1423 which w er e attributed to the compositions that ultimately control the specific molecular arrangement and the potential to bond to the su rface of the slide The morphology of each grafted surface was heterogeneous as opposed to a uniform smooth layer This was interpreted as variations in molar mass. Molar Mass The grafted copolymers were cleaved off the glass surfaces. The mol ar mass was d etermined by the GPC The number average mol ar mass (M n ), the weight average

PAGE 80

80 mo lar mass (M w ), and the polydispersity (PD) of 3421, 3241, 3340, 3214, and 1423 were shown in Table 4 7 The mol ar masses of the copolymer s ranged from 4 .1 k g/mol to 6 .9 k g/mol w ith the PD close to 1.2. T he molar mass is important since it impacts the morphology and the surface energy of the grafted surface. These factors are known to influence bio adhesion of bacteria, proteins, and cells to surface s 12,45,65 Zoospore Settlement and Release on Copolymer grafted Glass Slides Leaching test was examined by UV spectrophotometer using sample 3421 as the standard The adsorption appeared at 190 nm and the intensity increased with in creasing concentration of the standard. The adsorption intensities (Figure 4 4) of all copolymers were far below the intensity of the 1 ppm standard, which indicated the concentrations from leaching test were much lower than 1 ppm. Spore settlem ent densiti es were lower on all the acryla te based samples than on the PDMSe standard (Figures 4 5 a ). 3214 and 3340 showed the best antifouling efficiency ( 9 2 % reduction to PDMSe standard ). 3421 and 1423 exhibited a reduction of 83% and 86%, respectively. Spore settlement densities generally de creased with in creasing hydrophilicity (R 2 = 0.60) (Figure 4 6 ). If we compare only the five copolymer grafted surfaces without the standards (the glass and PDMSe slide) s pore settlement densities de c reased with in c reasing hydrophilicity on samples 3214, 3421, 1423 and 3241 However, the least hydrophilic sample, 3340 had the lowest settlement density. The lack of a clear relationship with hydrophilicity is possibly due to the narrowness of the contact angle range b etween these copolymer grafted surfaces The lowest water contact angle was 30.5 and highest was 51 3 representing a difference of only 20.8

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81 Spore removal occurred on ly on 3421 (47%) and 3241 (59%) (Figure 4 5 b ). It is hard to tell the wettabilit y or ch emical compositions that might have caused the high removal from them. Both surfaces contained low proportion (10%) of PAMPS, but for the surfaces containing even lower proportion (0%) of PAMPS (3340) and higher proportion (40%) of PAMPS (3214) did not sho w any spore removal from the surfaces. T he low spore settlement densities on all the copolymer grafted surfaces make this acrylate copolymer a promising group of marine antifouling materials. The excellent antifouling nature of acrylate based copolymers is comparable to the most recent published marine antifouling coating materials, such as poly(sulfobetaine) coated surfaces 65 and poly(ethylene gly col) containing hydrogel surfaces 31 Zoospore Settlement and Release on Copolymer grafted PDMSe Slides Two acrylate c ompositions (3340 and 3214), which had the best antifouling (92% reduction) against zoospores on glass slides were chosen to graft o nto smooth PDMSe and Sharklet TM PDMSe. The s pore settlement densities (Figure 4 7 ) on both smooth acrylate grafted PDMSe surface s (SM 3214 and SM 3340) were lower than on the smooth PDMSe standard which showed 80% reduction and 87% reduction, respectively to smooth PDMSe (SM T2). However, the response of the zoo spores to the S harklet pattern on the two acrylate coatings differed markedly from each other. In the case of the 3214 copolymer the S harklet pattern increased spore settlement density, whil e on the 3340 the Sharklet pattern decreased the spore settlement density There was no statistical difference between SK 3214 and SK T2, indicating that the SK 3214 did not show a better fouling resistance than the SK T2. This is most likely due to the cop olymer chains burying into PDMSe network while the surfaces were exposed to the air for one day. This is evident

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82 by the water contact angle changes (from 76 to 92 ). All the other samples were kept in the water all the time before the zoospore assay. The SK 3340 had the most fouling resistance to zoospores, which was 97% reduction compared to smooth PDMSe (SM T2). Initial Attachment and Strength of Navicula diatom on Copolymer grafted PDMSe Slides The initial attachment densities of the Navicula diatoms o n the copolymer grafted PDMSe slides were all lower than on the smooth PDMSe (SM T2) (Figure 4 8 ). Both 3214 coatings (SM 3214 and SK 3214) showed lower attachment densities than 3340 coatings on either smooth or Sharklet. The lowest attachment densities w ere on the SM 3214 which showed 87% reduction to smooth PDMSe (SM T2). T he addition of the S harklet pattern reduced attachment densit ies on the PDMSe by 34 % and to a lesser extent on the 3340 coatings (18 %). However, on the 3214 coating the density of a ttached cells was slightly raised Diatom removal after a shear stress of 26Pa was substantially higher on all copolymer grafted PDMSe surfaces (60 80% removal) than on the smooth PDMSe ( 10% removal ) (Figure 4 9 ). T he S harklet patterning caused a slight increase in diatom removal for the unmodified T2, 3340 and 3214 grafted surfaces The remaining cell densities on the copolymer grafted PDMSe surfaces after application of 26 Pa shear force ( Figure 4 10 ) were all greater than 93% reduction compared to T2 except for the SM 3340, which had an 82% reduction. The low Navicula diatom attachment densities on all of the acrylate based copolymers make this a promising group of marine antifouling materials.

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83 Summary Copolymers of acrylic acid (AA), a crylamide (AAm), methyl acrylate (MA), and 2 acrylamido 2 methyl propanesulfonic acid (AMPS) were grafted onto silicate slides using thiol ene polymerization The surfaces were examined by XPS to determine the chemical composition of each monomer present on the surface The chemical compositions of all five copolymer grafted surfaces were similar to the initial solut ion monomer ratio s The surfaces were also examined by a goniometer with both static and dyn amic contact angle measurements. Both OWK and LW AB methods were used to calculate the surface energ ies of the copolymer grafted slides and yielded a surface energy of 53.1 62.6 mJ/m 2 This range of surface energies indicates a possible route to tune the surface energy by chang ing the acrylate component ratio. All of t he acrylate copolymer samples had much lower settlement densities tha n the PDMSe standards. The lowest settlement densities had a 9 2 % reduction (3340 and 3214) compared to PDMSe When combined with the Sharklet topography (+2.8SK2x2), the lowest settlement densities reached 97% reduction (SK 3340) compared to PDMSe. S ettlement densities generally decreas e with increasing surface wetting These acrylate samples also exhibited great AF and FR properties on Navicula diatoms. The acrylates samples showed as hi gh as 87% less attachment to T2 standard in the initial attachment assay and more than 60% removal after exposed to a shear stress of 26 MPa. The remaining cell densities on the acrylate samples were all greater than 93% reduction compared to T2 except for the SM 3340, which had an 82% reduction. The low Ulva zoo spore and Navicula diatom settlement densities on all of the acrylate based copolymers make this a promising group of marine antifouling materials.

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84 Table 4 1 Initial solution and the final surface compositions of sample s 3421, 3241, 3340, 3214, and 1423. Table 4 2 XPS composition and high resolution data of S MTS, sample s 3421, 3241, 3340, 3214, and 1423

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85 Table 4 3 Static sessile drop water (WT), diiodomethane (DM) and glycerol (GL) contact angle s and dynamic (advancing and receding) WT contact angle s of S MTS and sample s 3421, 3241, 3340, 3214 and 1423. Ten and five drop s were measured on each sample for sessile drop and dynamic contact angle respectively. The value s are expressed as average standard deviation. Table 4 4 The liquid surface tension ( L ) of WT, DM, GL and their corresponding components: polar ( L P ), dispersion ( L d ), Lifshitz L LW ), Lewis L + ), Lewis L ) and acid L AB )

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86 Table 4 5 The S ), polar and dispersion component s S P S d ) values of S MTS and copolymer grafted samples calculated with the OWK method Table 4 6 The surface energ y S ), Lifshitz S LW S + ), S ) and acid S AB ) parameters of S MTS and copolymer grafted surface s calculated from LW AB method.

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87 Table 4 7 The number average mol ar mass (M n ), weight average mol ar mass (M w ) and polydispersity (PD) of 3421, 3241, 3340, 3214, and 1423. Figure 4 1.

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88 Figure 4 2 Grafting copolymers onto a glass slid e. A ) hydrolysis of a glass slide. B ) coupling of MTS C ) gra fting acrylate based polymers

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89 Figure 4 3 AFM ty pical images (amplitude mode). A ) 3421. B ) 3241. C) 3340. D ) 32 14. E ) 1423.

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90 Figure 4 4 The leaching test measured by UV using sample 3421 copolymer as the reference

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91 Figure 4 5 Ulva zoospore assay on the copolymer grafted glass slides A ) Density of settled spores. B ) The remov al of spores *= statistical different

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92 Figure 4 6 Density of settled spores on the standards and the five copolymer grafted surfaces plotted as a f unction of static water contact angle Figure 4 7 Density of settled spores on the copolymer grafted PDMSe slides (SM: smooth; SK: Sharklet TM ). *= statistical different

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93 Figure 4 8 The initial attachment density of Navicula on the copolymer grafted PDMSe slides *= statistical different groups Figure 4 9 The removal of Navicula from the copolymer grafted PDMSe slides *= statistical different groups

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94 Figure 4 10 The remaining diatom attachment densit ies on the copolymer grafted PDMSe slides. *= statistical different groups.

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95 CHAPTER 5 PEGYLATED BRUSH ARCH ETECTURE ON ANTIFOUL ING AND FOULING RELEASE AGAINST ULVA ZOOSPORES Introduc tory Remarks P oly(ethylene glycol) (PEG) functionalized polymers are widely used for the advantages of its hydrophilicity, non toxicity and reducing the adhesion of proteins, cells and bacteria 36 Studies of the PEG on protein resistance were reported. 12,37,41,82 A number of theoretical considerations suggest that the great entropic repulsion between t he PEG surface and the protein is the main reason for the protein resistant phenomenon. 63 The entropic repulsion is due to the rapid movement of the PEG hydrated chains. This viewpoint is confluent with the perspective brought up by McPherson et al. 64 who belie ved that the protein adsorption prevention is due to the steric effect which PEO segments block the adsorption sites of the surface. T he formation of a biofilm starts from the formation of a co ndition ing film, which is generally composed of organic materia ls such as proteins and carbohydrate compound 1 Then, the bacteria come to contact with this conditioning film to develop a bacterial biofilm, which is followed by spores of macroalgae, i.e., Ulva linza ,or other fungi within a week. 74 This stepwise model is a general view of fouling strategies 74 In reality, Ulva zoospores behave in a dynamic way and could also settle on a clean surface within a few minutes of immersion. 15 Despite the case of zoospores cable of settlement on a clean surface directly, most studies revealed that the init ial biofilms, such as protein and bacterial layers have significant influences on the fouling of spores. 1,74 Ulva zoospores is one of the common marine fouling organisms, which prefer to settle on a hydrophobic surface rather than a hydrophilic surface 34 The PEGylated

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96 polymer is hydrophilic. Studies of the PEG functionalized materials on the antifouling against Ulva zoospores were relatively less compared to those against proteins. Schilp et al. made self assembled monolayers (SAMs) of hexa(ethylene glycol) 13 showing the spore density decrea sing with increasing wettability. Ekblad et al. synthesized a random copolymer composed of the oligo ethylene glycol methyl ether methacrylate (OEGMEMA) and the hydroxyl ethyl methacrylate (HEMA). This copolymer is in a linear fashion. A 92% reduction of z oospore density to PDMSe was achieved. Other PEG related coatings for the current marine fouling research were amphiphilic based materials, which are composed of both fluoronated and PEG segments. 45,70,102 Many of these studies were focusing on copolymerizing PEGylated polymers with other type of polymers to make a chemical complexity on a su rface to optimize the antifouling and fouling release properties. In the studies above, the effect of PEG polymer chain architectures in terms of PEG side chain length, brush molar mass, and film thickness on Ulva zoospore settlement and release was not di scussed yet. In this study, the architecture of the grafted PEG polymer, i.e., poly(oligo ethylene glycol) methyl ether methacrylate (POEGMEMA), was altered by the OEGMEMA monomers with selected OEG side chain lengths and by degree of polymerizati on. We chose three levels of OEG side chain length (n=9, 19 and 45) and two level s of degree of polymerization ( [OEGMEMA] = 50 mM and 100 mM ) By combination of both factors the coating surfaces with different film thicknesses, and brush molar masses were created. These components were evaluated to determine the contribution in the bioresponse of zoospores.

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97 Experimental Section Materials M icroscope glass slides (76mm x 25mm x 1mm) hydrogen peroxide (50 wt.% solution in H2O ), pyridine (>99%), tetrahydrofuran (99.9%, extra dry), ethyl acetate (99.5%, HPLC grade), n hexane (> 98%, extra dry), trichlorosilane (98%) 10 undecen 1 ol (98%) 2 bromoisobutyryl bromide (98%) and hydrochloric acid (12.1M) were purchased from Fisher. Oligo (ethylene glyco l) methyl ether methacrylate (Mn=300, 950, 2080g/mol) (OEGMEMA 300, OEGMEMA 950, OEGMEMA 2080), 2,2 bipyridine(>99%) (BIPY), bromoisobutyrate (98%) (EBIB), Copper(l) Bromide (99.999%) (CuBr) were purchased from Aldrich. Platinum divinyltetramethyld isiloxane (Karsted t s catalyst CAS 68478 92 2) was purchased from Gelest Nanopure deionized (DI) water (18 .1 cm) was produced in house. The surface initiator, (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS) was synthesized as desc ribed below. Synthesis of (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS) The surface initiator, (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS) was synthesized by a two step reaction, in which 10 Undecen 1 yl 2 bro mo 2 methylpropionate is an intermediate product (Figure 5 1). Synthesis of 10 Undecen 1 yl 2 bromo 2 methylpropionate : 10 undecen 1 ol (82 mmol) was added into a well stirred mixture of THF (80 mL) and pyridine (86 mmol) in a round bottom flask (500 mL). 2 Bromoisobutyryl bromide (82 mmol) was slowly added into the mixture in 10 minutes. The flask was then wrapped with al uminum foils and let the reaction occur in dark at 22 C for 16 hours. An amount of 50 mL hexane was

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98 added into the flask a fter the THF was evaporated using a rotary evaporator. The mixture was washed with 1M HCl (75 mL) two times followed by DI water (75 m L) three times. The flask was connected with a rotary evaporator again to evaporate hexane. The liquid product was passed through silica gel chromatography (n hexane : ethyl acetate = 2 : 1 (v/v)). During purification, the product was confirmed using thin layer chromatography (TLC). The solvent was removed under vacuum to give the product (25.95g, 99.4% yield). The chemical structure was confirmed by 1 H NMR (Figure 5 2). 1 H NMR (300 MHz, CDCl 3 ) : 1.21 1.45 (br m, 12H); 1.62 1.74 (m, 2H); 1.93 (s, 6H); 2.05 (q, 2H, J=6.6 Hz); 4.16 (t, 2H, J=6.6 Hz); 4.89 5.03 (m, 2H); 5.73 5.88 (m, 1H) ppm. Synthesis of (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS): 10 Undecen 1 yl 2 bromo 2 methylpropionate (90 mmol) was put i nto a round bottom flask (500 mL ) with a magnetic stir bar. Trichlorosilane (300 mmol) and Karstedt s catalyst ( Platinum divinyltetramethyldisiloxane 0.1 g) were added into the flask. The flask was tightly sealed after purged with nitrogen for 2 minutes. The flask was wrapped wit h aluminum foils and let the mixture stirred in dark at 22 C for 24 hours. The excess trichlorosilane was removed under reduced pressure. The mixture was further dried in vacuum to give a clear yellow liquid (26.3g, 96.7% yield). The chemical structure was confirmed by 1 H NMR (Figure 5 3). 1 H NMR (300 MHz, CDCl 3 ) : 1.25 1.44 (m, 16H); 1.52 1.73 (m, 4H); 1.90 (s, 6H); 4.14 (t, 2H, J=6.6 Hz) ppm. Methods Coupling initiators onto a glass s urface Microscope g lass slide s were preconditioned by a flame treatment. Each slide was passed through the flame of a B unsen burner 3 times slowly. The slides were cool ed for

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99 3 minutes at room temperature and then p laced in a glass coplin jar containing an aqueous solution of hydrochloric acid (4.7N) and hydrogen per oxide (8.4N). The slides were sonicated (Bra n son 3210) in the jar for 1 hour. E ach slide was subsequently washed twice with 25 m L DI water The cleaned slides were stored in DI water before coupling initiators onto glass surfaces A 2 % (v/v) BrPUTS /toluene solution was prepared and added to a staining dish with the dried clean slides in the slide rack. The reaction was carried out for two hours with the stirred solution The slides were rinsed with approximately 1 5 mL toluene, dried with a stream of nitroge n for 10 seconds and then stored in centrifuge tube s prior to ATRP grafting The successful coupling of BrPUTS was confirmed by X ray photoelectron spectroscopy (XPS) with the appearance of Br peak in the survey scan (Figure 5 4). ATRP g rafting The BrPUTS coupled slides were placed in a staining dish within the slide rack. The glass cover of the staining dish was substituted by a silicone cover (5 mm in thickness) which was cast against the dish top using Silastic T2 poly(dimethylsiloxane) elastomer (PDMSe). This silicone cover allowed for injection of chemicals without the exposure of the system to the air. It also allowed for keeping the system in an inert gas environment with a minimized inert gas supply during the reaction. The reaction mixture wa s started by first add ing methanol (160 mL ) and BIPY (8 mmol) and stirred with a magnet bar. After BIPY was dissolved completely, the OEGMEMA 300 or OEGMEMA 950 or OEGMEMA 2080 (10 mmol or 20 mmol) and DI water (20 mL ) was added into the mixture. The mixtu re was purged with N 2 for 30 minutes before a careful addition of CuBr (4 mmol) under N 2 and injection of EBIB (0.2 mmol) from the PDMSe cover. After

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100 CuBr was dissolved in the mixture, the color turned dark red. The reaction lasted for at least 24 hours un til all the OEGMEMAs were consumed. A more than 99% conversion of PEGMEMAs was confirmed by the disappearance of the peak at :5.4 5.8 ppm in the NMR. 103 Surface c haracterization Contact a ngle and s urface e nergy m easurement : The equilibrium c ontact angle of a sessile drop ( 5 L ) was measured with a Rame Hart model 500 goniometer for each grafted surface The average contact angle was determined by measurement of ten drops. The Owens Wendt Kaelble (OWK) method 80 was used to calculate surface energies. The contact angles were measured using the water (WT, = 72.8 mN/m, = 51.0 mN/m, = 21.8 mN/m) as a polar probe liquid and the diiodomethane (DM = 50 .8 mN/m, = 1.3 mN/m, = 49.5 mN/m) ) as a non polar probe liquid. T he polar ( S P ) and dispersion ( S d ) components of the surface energies were deter mined by E q. 5 1 and E q. 5 2. ( 5 1) ( 5 2) The paramet ers and refer to the total surface tension, dispersion and polar components of the probe liquid, re spectively. The s urface energ y ( ) of a modified surface is the sum of polar ( ) and dispersion ( ) components of the solid. XPS: The XPS was used to analyze the surface chemical composition of POEGMEMA 300, POEGMEMA 950 and POEGMEMA 2080. The spectra were

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101 recorded using Perkin Elmer PHI 5100 ESCA system with a magnesium samples were analyzed at 45 take off angle under ultra high vacuum ( ~ 2x 10 9 Torr). Both survey scans (0 1100eV) and high resolution of C1s spectra were performed to determin e the element composition. Both analyses and curve fitting were performed on AguerScan 3.2 (RBD instru ment) Ellipsometry: A n ellipsometry (FILMetric F20) coupled with FILMeasure software was used to measure the thickness of the grafted POEGMEMA brushes. A s ilicon wafer of (100) orientation which was grafted with POEGMEMA in the same manor, was used to estimate the thickness of POEGMEMA brushes on glass slides. 82 The data from five spots of each sample were averaged and reported as mean standard deviation. TM AFM : A TM AFM was utilized to anal yz e the surface morphology and roughness. The data were recorded by VEECO Dimension 3100 equipped with a Nanoscope III controller under tapping mode using a silicon pyramidal tip (10nm in diameter). The scan rate was se t at 1.0Hz and the scan size was set at 2 m. A value of RMS roughness was calculated from the roughness profile of the scanned area using the Nano scope software 7.0. Mol ar m ass d etermination of g rafted POEGMEMA The mo lar mass of grafted POEGMEMA brushes w as estimated by measuring the POEGMEMA in the solution from the free initiator (EBIB). We assumed that the molar mass of the grafted brushes is close to that formed from free initiator. This assumption has been shown valid for grafting methacrylate based polymers, such as POEGMEMA, poly(2 methacryloyloxyethyl phosphorylcholine and poly(2 hydroxy ethyl methacrylate) using ATRP. 60,104,105 T he mol ar mass was determined with Waters GPC Model V2K

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102 using HPLC grade TH F as an eluent. The instrument w as calibrated using poly ( styrene ) standards with polydispersities less than 1.1 Ulva z oospore s ettlement and f ouling r elease a ssays Leaching t est : S am p les were soaked in the DI water for 24 hours at 2 2 0 C for leaching test. The water was examined by UV spectrophotometer to determine if POEGMEMA were present. The POEGMEMA 300 with gradient concentrations (10 ppm, 5 ppm and 1 ppm) was used to create the calibration curve Settlement and r elease of z oospores : Six replicates of each polymer grafted surface were prepared. Silastic T2 PDMSe coated slides were as standards in this experiment. There were six replicates used in the Ulva spores settlement assay (3 replicates) and release assay (3 replicates) The as says were performed as described previously 97 Briefly samples were immersed in the artificial sea water (ASW) (Instant Ocean ) for 2 hours before the assay. A 10 mL aliquot of spore solution ( 1.5 x 10 6 spores/m L ) was added into a Petri dish and incubated in the dark for 45 minutes at 20 0 C. The samples were gently rinsed with ASW to remove unattached spores and fixed with 2% glutaraldehyde in seawater for 10 minutes The number of spore s was count ed using an image process system connecte d to a fluorescence microscope. The mean spore density was determined based on 30 fields of view (0.15 mm 2 ) on each of the three slides. For release assays, a turbulent flow apparatus providing a shear stress of 50 MPa was applied to the other three unfix ed slides The spores remaining on the slides were fixed and counted. The remaining spore density was determined using the same method described above.

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103 Results and Discussion Contact Angle and Surface Energy Three different PO EGMEMA (PEOGMEMA 2080, PEOGMEMA 950, and PEOGMEMA 300) with two levels of concentration (L: 55 mM; H: 110 mM) were grafted onto glass slides. The water contact angles (Table 5 1 ) were consistent with those reported in the literature (35 55 ) 36 confirm ing the presence of grafts. All grafts with high concentratio n level of each POEGMEMA monomer performed lower contact angles than those of low concentration level. The POEGMEMA 300 H exhibited the lowest contact angle ( 3 3 9 3.3 ), which was different from POEGMEMA 2080 H and POEGMEMA 950 H, which showed contact angles of 3 9.5 1.8 and 3 8.6 3.4 respectively and no statistical difference (one way ANOVA, =0.05 ). For low concentration grafts, POEGMEMA 2080 L exhibited the highest water contact angle (48.3 2.9 ) while POEGMEMA 950 L (42.5 1.9 ) and POEGMEMA 300 L (43.9 3.4 ) showed lower contact angles with no statistical difference (one way ANOVA, =0.05 ) between them. This result suggested that POEGMEMA 300 H formed the most hydrogen bonds with water. The surface energy was calculated by the OWK method in which a polar nonpolar pair of liquids, i.e., water diiodomethane (WT DM) w as used to measure the contact angle. The POEGMEMA 300 H had a highest surface energy S =66 mN/m) (Table 5 1 ) among the all surfaces. The second higher surface en ergies were on another two grafts with high concentrations, POEGMEMA 2080 H and POEGMEMA 950 H, which had surface energies of 63.5 mN/m and 63.4 mN/m, respectively. All the other grafts with

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104 low concentration, POEGMEMA 2080 L, POEGMEMA 950 L and POEGMEMA 3 00 L, had lower surface energies of 59.3 mN/m, 60.8 mN/m and 60.2 mN/m, respectively. The d ynamic water contact angles (Table 5 2) showed that the POEGMEMA 2080 H and POEGMEMA 2080 L had high contact angle hystereses of 55.3 and 54.3 respectively compared to the POEGMEMA 950 (H and L), and POEGMEMA 300 (H and L), which ranged from 21.7 29.7 The notable high hysteresis of POEGMEMA 2080 was due to the low receding contact angle values, which was ~ 5 (Figure 5 5 ) TM AFM The roughness and morpho logy of the grafted surfaces were evaluated using TM AFM as shown in Figure 5 6. The morphology of POEGMEMA 2080 H and L (Figure 5 6 (A) and (B)) showed elongated ridges across each other, which was distinctly different from the bulge like morphologies o bserved from POEGMEMA 950 and POEGMEMA 300 series. This elongated morphologies formed most likely due to the long side chain (n=45) of PEGMEMA 2080. It is suggested that the formation of the elongated ridge like morphology was due to the stack up of OEG si de chains from strong inter molecular interaction by hydrogen bonds. The calculated RMS roughness values were greater on POEGMEMA 2080 H and L (28.1nm and 28.4 nm). The roughness decreased with decreasing monomer side chain length, i.e., POEGMEMA 950 H (1 6.5 nm), POEGMEMA 950 L (15.9 nm), POEGMEMA 300 H (16.4 nm), and POEGMEMA 300 L (13.0 nm). The degree of polymerization which was controlled by the monomer concentrations did not influence much of the roughness on the grafted surface s. The morphology of e ach grafted surface was heterogeneous which was interpreted as variations in molar mass

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105 XPS The existence of a POEGMEMA grafted surfaces were supported by the XPS measurement. XPS C1s high resolution spectra revealed the dependence of the surface compos ition of POEGMEMA 2080, POEGMEMA 950, and POEGMEMA 300 with side chain lengths of n= 45, 19, and 5, respectively. The spectra of low concentration POEGMEMA 300, 950 and 2080 (Figure 5 7) clearly demonstrated three distinct peaks corresponding to the ester O C = O (289.0 eV) the ether C O (286.5 eV) and the aliphatic C C / C H (285.0 eV) in each of POEGMEMA structure. The intensity of the C O (286.5 eV) increased with respect to the O C = O (289.0 eV) and C C / C H (285.0 eV) as the side chain length increased. The calculated spectral area ratios of the three peaks were in agreement with the theoretical ratios for all three POEGMEMA grafted surfaces (Table 5 3). The possible reason for the deviation of the calculate d peak ratio from the theoretical ratio is the adventitious carbon contaminants produced during sample preparation prior to XPS measurement. Film Thickness and Molar Mass The ellipsometric thicknesses ( Table 5 4) of POEGMEMA 2080 L, POEGMEMA 2080 H, POEGME MA 950 L, POEGMEMA 950 H, POEGMEMA 300 L, and POEGMEMA 300 H were 2 5 2 nm, 51 2 nm, 2 2 2 nm, 30 2 nm, 18 2 nm, and 23 3 nm respectively. An increased thickness was observed for the POEGMEMA with a longer side chain length and high concentration. The film thickness was associated with the molar mass of grafted polymers. The measured molar masses of each POEGMEMA grafted surface were tabula ted in Table 5 4. The measured number average molar mass of POEGMEMA 2080 H was 30.2 kg/mol, which is approximately twofold that of POEGMEMA 2080 L (Mn = 15.7

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106 kg/mol). This value was reasonable since the monomer concentration of H series was twice as muc h as L series, and the reaction was carried out more than 99% conversion (examined by NMR by the decay of :5.4 5.8 ppm) 103 This molar mass relation was also true for POEGMEMA 950 and POEGMEMA 300, i.e., the molar mass of POEGMEMA 300 H (Mn = 5.6 kg/mol) was twice as much as that of PO EGMEMA 300 L (Mn = 2.7 kg/mol). The molar mass of the grafted polymer was proportional to the side chain length of the monomer if we considered the same degree of polymerization. For instance, the molar mass of POEGMEMA 2080 H (Mn = 30.2 kg/mol) was approx imately twice as much as that of POEGMEMA 950 H (Mn = 15.4 kg/mol). A low polydispersity (PD < 1.1) of final synthesized polymer was expected s ince ATRP has a living feature during the polymerization. In this stud y, POEGMEMA 2080 and 950 series had poly dispersities less than 1.1; however, POEGMEMA 300 series had greater PDs (1.41 for POEGMEMA 300 L and 1.27 for POEGMEMA 300 H). This was interpreted as the relatively high propagation rate of OEGMEMA 300 monomer to the activation/ deactivation rate of Cu co mplex. This high polydispersity on the POEGMEMA with short side chains synthesized by ATRP was also observed by Fan et al.. 43 Ulva Zoospores Settlement and Release Assay T he spore s ettlement densities were shown in Figure 5 8 The spore settlement density de creased as the POEGMEMA side chain length in creased for the three low monomer concentration POEGMEMA i.e., the spore density of POEGMEMA 2080 L < POEGMEMA 950 L< POEGMEMA 300 L However, this trend was not seen on the three high m onomer concentration of POEGMEMAs The spore settlement densities

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107 increased as the POEGMEMA side chain length decreas ed between the POEGMEMA 2080 H and POEGMEMA 2080 L, but showed an opposite result between the P O EG MEMA 950 H and POEGMEMA 300 H. The lowest settlement density was on POEGMEMA 2080 L and POEGMEMA 300 H. Spore removal was low on all POEGMEMA grafted surfaces (Figure 5 9 ) except the P O EG MEMA 950H and P O EG MEMA 300L The percentage removal was only 14% for POEGMEMA 950 H and 22% for POEGMEMA 300 H. Th is low removal data made it difficult to compare the spore adhesion strengths between the POEGMEMA grafted surfaces based upon their particular chain molar mass, side chain lengths, and brush thicknesses. Discussion The antifo uling and fouling release properties of the P OEGMEMA grafted surfaces were investigated by the settlement and release assay of Ulva zoospores. In this assay, the zoospore settlement densities on PDMSe slides were approximately half lower than that on the glass slides, which was abnormal as what we ha ve seen before. It is evident in Brennan_Report_12_2010, which the spore densities on PDMSe were more than three fold of the densities on glass slides. In the Brennan_Report_18_2010, the zoospore densities on PDMSe were even more than four fold of the dens ities on glass slides. Therefore, it would be problematic to compare the spore densities on the POEGMEMA grafted surfaces to the PDMSe standard. However, these data are still valuable if we compare merely the six POEGMEMAs The spore densities showed a neg ative trend (R 2 =0.96) with the side chain lengths (n=9, 19 and 45) (Figure 5 10) in low monomer concentration. If we assume that the fouling resistance to the non specific proteins is correlated to the fouling resistance to

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108 the zoospores, then this trend w as in agreeme nt with that reported by Fan et al.. 43 They investigated the effect of P O EG MEMA side chain l ength s on 3T3 fibroblast cell adhesion The result show ed a higher fouling resis tance for longer EG side chains However, an opposite trend was observed in high monomer concentration series (H series). This is due to the low spore density of POEGMEMA 300 H causing the slope of the regression line to be positive. The zoospore settlement densities generally decreased with increasing POEGMEMA brush thickness (Figure 5 11). The brush thicknesses of the six POEGMEMA s in this study ranged from 18 nm to 51 nm. The information on Ulva zoospores response to the brush thickness has been limited to a few studies on the short chain P EGs prepared by SAMs. Schilp et al. synthesized hydroxyl terminated short chain PEGs with dif ferent ethylene glycol (EG) units, i.e.,EG 1 OH, EG 2 OH, EG 3 OH, EG 4 OH, and EG 5 OH. 106 The brush thicknesses ranged from 13 nm to 23 nm. The highest spore density was found on the surface (EG 1 OH) w ith the least thickness of 13 nm. A general trend that the spore densities decreased with increasing brush thickness was in agreement with our result. The plot of spore densities versus brush molar mass (Figure 5 12) showed a similar trend as observed in F igure 5 11. The spore densities decreased as the brush molar mass increased. A study has been shown that a coated surface with more EG units increased the resistance to spore settlement. 106 T his is most likely due to the strong steric repulsion along with the hydration of the films. The steric repulsion and surface hydration are strongly associated with the POEGMEMA chain architecture

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109 which is defined by brush molar mass, brush thickness and POEGMEMA side chain length. Settlement of Ulva zoospores on the POEGMEMAs generally decreased with increased surface free energy (Figure 5 13). The lack of a clear correlation (R 2 =0.08) with surface energies wa s probably due to the narrowness of the surface energy range between the POEGMEMAs The lowest surface energy was 59.3 mN/m and the highest was 66.0 mN/m representing a difference of only 6 .7 mN/m Despite the low correlation with the surface energy, the trend shown in this study was still in agreement with the study presented by Bennett et al. 73 who showed that the spore densities were negatively correlated (R 2 =0.80) with the surface energies (25 mN/m 55 mN/m) on xerogels. A recent research has shown that the water contact angle hysteresis plays a role on marine fouling release properties. Ikrime et al. 107 selected a series of polyolefins, having similar surface energies (30.2 mN/m 37.4 mN/m). Fouling release properties were found to positi vely correlate with surface contact angle hysteresis. The optimal percent removal (35.2%) was performed on a surface with contact angle hysteresis of 45 However, this phenomenon was not seen in our study. POEGMEMA 2080 H and POEGMEMA 2080 L had rather hi gh contact angle hystereses (55.3 and 54.3 respectively ) than the POEGMEMA 950 ( L and H) and POEGMEMA 300 ( L and H), which ranged from 21.7 29.7 However, both the POEGMEMA 2080 L and H did not exhibit any removal of spores from the surface. After careful observation of the surface morphologies, POEGMEMA 2080 surfaces had a finer roughness (RMS roughness=28 nm) than that of polyolefins (RMS roughness=76 nm). This roughness

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110 difference, a s well as chemical composition difference, may be the reason for the discrepancy of the spore removal on the two different types of materials. Summary We have demonstrated the preparation of six different POEGMEMA grafted surfaces (POEGMEMA 2080 L and H, POEGMEMA 950 L and H, and POEGMEMA 300 L and H) having close surface energies (59.3 mN/m 66.0 mN/m) but different molar masses, side chain lengths and film thicknesses. The dynamic contact angle measurements showed rather high hystereses on POEGMEMA 2 080 L and H (~ 55 ) than on POEGMEMA 950 and 300 (22 29 ). The chemical structures of POEGMEMA with different side chain lengths were measured and confirmed by the XPS. An increase of film thickness was observed for POEGMEMAs with the longer side chain lengths and the higher degree of polymerization. The surface roughness increased with increased POEGMEMA side chain length but was less dependent on the degree of polymerization, i.e., the roughness of POEGMEMA 2080 L and H was close to each other. Spore settlement densities showed marked differences between the POEGMEMA side chain lengths, but only weak correlations were found between film thicknesses, brush molar masses and surface energies. Although these were weak correlations, they followed the trend s as reported in the literature. We hypothesized that a surface with a high contact angle hysteresis would cause a higher release of spores compared to a surface exhibiting a low hysteresis. The fouling release assay result failed to comply with this hypot hesis. We suggested that there are factors affecting the release of spores other than the hysteresis. The factors such as the surface roughness and the chemical composition play a role on this issue.

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111 Table 5 1. Sessile drop contact Angles, surface s ), polar, and dispersion S P S d ) values of POEGMEMA grafted surfaces calculated by Owens Wendt Kaelble method. WT: water; DM: diiodomethane Table 5 2. adv rec ), and adv rec ) of POEGMEMA grafted surfaces Table 5 3. Measured subband binding energies and the theoretical ratios of grafted POEGMEMA 2080, POEGMEMA 950 and POEGMEMA 300.

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112 Table 5 4 The brush thicknesses, number average molecular we ight (M n ), weight average molecular weight (M w ), and polydispersity (PD) of POEGMEMA grafted surfaces.

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113 Fig ure 5 1. Synthesis of A 10 Undecen 1 yl 2 bromo 2 methylpropionate and B. (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS)

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114 Fig ure 5 2. 1 H NMR of 10 Undecen 1 yl 2 bromo 2 methylpropionate.

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115 Fig ure 5 3. 1 H NMR of (11 (2 Bromo 2 methyl)propionyloxy) undecyltrichlorosilane (BrPUTS)

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116 Fig ure 5 4. The appearance of Br in the XPS survey scan indicating the a successful coupling of BrPUTS onto a glass surface. Fig ure 5 5 Receding contact angles ( rec ) A) POEGMEMA 2080 H B) POEGMEMA 950 H C) POEGMEMA 300 H

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117 Fig ure 5 6 Three dimensional TM AFM images A ) POEGMEMA 2080 H B ) POEGMEMA 2080 L C ) POEGMEMA 950 H D ) POEGMEMA 950 L E ) POEGMEMA 300 H F ) POEGMEMA 300 L.

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118 Fig ure 5 7 XPS C1s spectra with curve fittings of POEGMEMA 2080 L, 950 L and 300 L Peak s : A : O C = O (289.0 eV); B : C O (286.5 eV); C : C C / C H (285.0 eV).

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119 Figure 5 8 Density of spores on PEG brush samples *= statistical different groups Figure 5 9 The removal of Ulva spores from PEG brush samples *= statistical different groups

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120 Figure 5 10 Density of spores versus PEG side chain lengths (n=9, 19 and 45) on L series and H series POEGMEMA samples Figure 5 11 Density of spores versus POEGMEMA brush thickness.

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121 Figure 5 12 Density of spores versus POEGMEMA molar mass. Figure 5 13 Density of spores versus surface energies of POEGMEMA samples.

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122 CHAPTER 6 CONCLUSIONS AND FUTURE WORK Conclusions Biofouling has been a co mplex problem that draws an economic and environmental concern. The motivation of this research is based upon a critical need for an effective marine antifouling and fouling release surface that is environmentally neutral. A thiol ene polymerization was used successful ly to graft to glass slide s and PDMSe by a simple 3 step syntheses This surface grafting provides a facile, cost effective and simple alternative method The ATR FTIR, XPS, TM AFM, GPC, an ellipsometry, and a goniometer were used to analyze the grafted surfaces and provide the chemical compositions, as well as physical properties such as surfa ce energies, surface morphologies, roughness, film thickness and molar mass. Low molar mass (Mn= 5 8 kg/mol) c opolymers consisting of acrylic acid (AA), acrylamide (AAm), methyl acrylate (MA), and 2 acrylamido 2 methyl propanesulfonic acid (AMPS) were gr afted onto silicate and PDMSe slides Chemical compositions were altered by mixing different ratios of these four monomers. The chemical compositions were further applied to PDMSe with the Sharklet TM topography. All the copolymer grafted surfaces were eval uated for their ant ifouling and fouling release properties with a marine organism Ulva zoospores. Two compositions of the acrylated grafted PDMSe surfaces were also evaluated using the other marine organism, Navicul a diatoms. All of the acrylate copolymer samples had much lower settlement densities tha n the PDMSe standards. The lowest settlement densities had a 9 2 % reduction (3340 and 3214) compared to PDMSe When combined with the Sharklet topography (+2.8SK2x2),

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123 the lowest settlement densities reached 97 % reduction (SK 3340) compared to PDMSe. S ettlement densities generally decreas e with increasing surface wetting However, the fouling release against zoospores of the acrylate grafted surfaces was not obvious. These acryla te samples also exhibited great antifouling and fouling release properties against Navicula diatoms. The acrylates samples showed as high as 87% less attachment to PDMSe standard in the initial attachment assay and more than 60% removal after exposed to a shear stress of 26 MPa. The rema ining cell densities on the acrylate samples were 93% lesser than on PDMSe except for SM 3340, which had an 82% reduction. The low settlement densities of Ulva zoo spore s and Navicula diatoms on all of the acrylate based copolymers make this a promising gro up of marine antifouling materials. We have also demonstrated the preparation of six different PEGylated polymer brushes (POEGMEMA 2080, POEGMEMA 950, and POEGMEMA 300 with two concentration levels each), which had close surface energies (59.3 mN/m 66.0 mN/m) but varied molar masses, side chain lengths and film thicknesses. PEGylated polymer brushes have been evaluated for their antifouling properties against the Ulva zoospores based on the side chain lengths, the brush thickness, and the brush molar mass Spore settlement densities showed marked differences between the POEGMEMA side chain lengths, but only showed weak correlations with the film thicknesses, and the brush molar masses. We hypothesized that a surface with a high contact angle hysteresis (~55 for POEGMEMA 2080L and H ) would result in a higher release of spores to a surface exhibiting low hystereses (22 29 for POEGMEMA 950 and 300 ). The fouling release

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124 assay result failed to comply with this hypothesis. We suggested that there are fact ors, such as surface roughness and chemical composition itself would affect the release of spores other than the hysteresis. Future Work Acrylate Copolymers Graft This work clearly showed the excellent efficacy of the acrylates copolymers (Mn= 5 8 kg/mo l) on the antifouling and fouling release against Ulva zoospores and Navicula diatoms. An enhanced fouling resistance was achieved by the combination of the acrylate chemistries with the Sharklet TM topography. The whole picture of the effectiveness of the acrylate copolymers on AF and FR should be further evaluated by testing these copolymers with other m i crofoulers such as bacteria, and macrofoulers such as barnacles and tubeworms. Future work should also focus on the molar mass of the acrylate grafts. Th e molar mass of the acrylate grafts in this research was slightly higher than that in the oligomer level. A reduced molar mass (2 5 kg/mol) would be of interest to see how the short chain oligomers with charges react with marine organisms. We hypothesize that short linear chains with short range repulsive forces would be more effective on preventing the settlement of zoospores or diatoms since the flocculation through bridging reaction, i.e., attractive forces, could be minimiz ed Other combination of co polymer grafts, which contain the electrolyte type or the zwitterionic type monomers could also be prepared to control the surface charge as well as hydrophilic/hydrophobic balance. It would be of interest to know how the microorganisms, i.e., zoospores in teract with a surface with various charge densities.

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125 This result could be applied for future design of copolymer combination s to prevent bio adhesion. PEG ylated Polymer Graft The zoos pore settlement assay has shown marked differences between the POEGMEMA side chain lengths, but only weak correlations were found between film thicknesses, and brush molar masses. The data of the film thickness and the brush molar mass in this study were prese nted using th ree different side chain lengths of POEGMEMA. Since both the side chain length and the degree of polymerization affect the final film thickness and brush molar mass, the future experiment should rule out the side chain length factor by using s ingle side chain length POEGMEMA at a greater range of monomer concentrations. Then, the effect of the film thickness and the brush molar mass on fouling resistance of zoospores could be investigated. The POEGMEMA 300 should be chosen for this as it showed the greatest difference in the spore settlement density between the low and high monomer concentrations

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126 LIST OF REFERENCES 1. Fusetani N, Clare AS. Antifouling Compounds. Berlin: Springer; 2006. 2. Champ MA. A review of organotin regulatory strategies, pending actions, related costs and benefits. Science of the Total Environment 2000;258(1 2):21 71. 3. Callow ME, Jennings AR, Brennan AB, Seegert CE, Gibson A, Wilson L, Feinberg A, Baney R, Callow JA. Microtopographic cues for settlement of zoospores of the green fouling alga Enteromorpha. Biofouling 2002;18(3):237 245. 4. Gudipati CS, Finlay JA, Callow JA, Callow ME, Wooley KL. The antifouling and fouling release perfomance of hyperbranched fluoropoly mer (HBFP) poly(ethylene glycol) (PEG) composite coatings evaluated by adsorption of biomacromolecules and the green fouling alga Ulva. Langmuir 2005;21(7):3044 3053. 5. Sui GD, Wang JY, Lee CC, Lu WX, Lee SP, Leyton JV, Wu AM, Tseng HR. Solution phase sur face modification in intact poly(dimethylsiloxane) microfluidic channels. Analytical Chemistry 2006;78(15):5543 5551. 6. Schumacher JF, Aldred N, Callow ME, Finlay JA, Callow JA, Clare AS, Brennan AB. Species specific engineered antifouling topographies: c orrelations between the settlement of algal zoospores and barnacle cyprids. Biofouling 2007;23(5):307 317. 7. Kristensen JB, Meyer RL, Laursen BS, Shipovskov S, Besenbacher F, Poulsen CH. Antifouling enzymes and the biochemistry of marine settlement. Biote chnology Advances 2008;26(5):471 481. 8. Kumar D, Aguilar GA, Chen JP, Butler GB, Brennan AB. A study of multi functional electrolytic oligomers as dispersants for concentrated aqueous alumina suspensions. Particulate Science and Technology 1999;17(4):317 332. 9. Kuo P l, Chuang T f; Yung Chi Paint & Varnish Mfg. Co., Ltd. (Kaohsiung, TW), assignee. Self polishing type antifouling coating composition containing film formable metal soap compound. US Patent. 1996. 10. Yasuyuki O, Toshihiko A, Junji N, Akihiro S; Chugoku Marine Paints, assignee. Antifouling coating material composition matching to freshwater environment, it's coated film and antifouling method. Japanese Patent patent JP2006070104 (A). 2006. 11. Malmsten M, Emoto K, Van Alstine JM. Effect of cha in density on inhibition of protein adsorption by poly(ethylene glycol) based coatings. Journal of Colloid and Interface Science 1998;202(2):507 517.

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135 107. Ucar IO, Cansoy CE, Erbil HY, Pettitt ME, Callow ME, Callow JA. Effect of contact angle hysteresis on the rem oval of the sporelings of the green alga Ulva from the fouling release coatings synthesized from polyolefin polymers. Biointerphases 2010;5(3):75 84.

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136 BIOGRAPHICAL SKETCH Jiun Jeng Chen was born in Taipei, Taiwan in 1978. He has two older brothers. Wh ile in Taipei, he attended Chung Shan elementary school in 1984, Ta Chi high school in 1990, Sung Shan senior high school in 1993. He graduated 2 nd in his school in 1996. Jiun Jeng went to National Taiwan University for his undergraduate degree in Chemical Engineering. He earned his living by being a tutor teaching high school math, physics and chemistry. In the summer of 2000, he joined Work & Travel program, sponsored by U.S. government and got a summer job in the Paramount Great America in San Jose, California. He met many international students at that time. This experience triggered his desire to travel around the world. In 2000, he enrolled in graduate school at National Taiwan Uni versity, still majoring in Chemical Engineering. Jiun Jeng worked in Professor Wen Yen Chiu s lab and gained polymer synthesis skills in her lab. He earned his master degree in 2002. Jiun Jeng started working in Chung Shan Institute of Science and Technolo gy, Taiwan in January 2003, which was part of his military service obligation. He served a product engineer for 3 years and project manager for a year. During the four years, he co nducted extensive research on design, fabrication and properties of fiber re inforced polymer (FRP) composites for thermal protection in missile system In 2007, Jiun Jeng was admitted into graduate school at the University of Florida in the Department of Materials Science and Engineering with an Alumni Fellowship. He worked under the advisement of Dr. Anthony B. Brennan, specializing in polymers. He rece 9 and his PhD in 2011.

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137 On June 20 th 2011, a very cute and lovely baby Jackson Okusa Chen was born and joined Jiun Jeng Chen and Shizuko Okusa s fami ly. This family is very special because all three members have different nationalities, Taiwanese, Japanese and American. He called his family an international family, which is a relatively small version of UN.