Amine Functionalization by Initiated Chemical Vapor Deposition (iCVD) for Interfacial Adhesion and Film Cohesion MASSACHUSETTS INSTITUTE OF TECHNOLOGY by JUN 13 2011 Jingjing Xu LiPAR CIES Master of Philosophy, Materials Science University of Cambridge, Cambridge, United Kingdom, 2006 ARCHIVES Bachelor of Engineering, Polymer Science and Engineering Beijing University of Chemical Technology, Beijing, China, 2005 Submitted to the Department of Chemical Engineering in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY IN CHEMICAL ENGINEERING AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2011 © 2011 Massachusetts Institute of Technology. All rights reserved. Signature of Author Department of'Chemical Engineering Mav23 201 1 Certified by Karen K. Gleason Professor of Chemical Engineering Thesis Supervisor Accepted by William M. Deen Professor of Chemical Engineering Chairman, Committee for Graduate Students Amine Functionalization by Initiated Chemical Vapor Deposition (iCVD) for Interfacial Adhesion and Film Cohesion by Jingjing Xu Submitted to the Department of Chemical Engineering on May 23, 2011 in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemical Engineering Abstract Amine functional polymer thin films provide a versatile platform for subsequent functionalization because of their diverse reactivity. Initiated chemical vapor deposition (iCVD) is a polymer chemical vapor deposition technique that utilizes the delivery of vapor- phase monomers to form chemically well-defined polymer films with tunable conformality and property. In this thesis work, amine functional iCVD poly(4-aminostyrene) (PAS) thin films were synthesized for the first time. The pendant amine groups enable the formation of a robust nanoadhesive with complementary epoxy functional groups. Bonded devices able to withstand >150 psi were achieved by combining polydimethylsiloxane (PDMS) and a wide variety of polymeric materials. Additionally, the all-iCVD nanoadhesive bonding process displays high resistance against hydrolytic degradation (>2 weeks). In addition to bonding, the iCVD layers remaining in the microfluidic channels provide functional groups for subsequent reaction and also act as diffusion barriers against oxygen permeation into the devices. Two applications utilizing this nanoadhesive bonding technique were introduced, including for growth of E. coli in the iCVD-bonded chips and fabrication of gas impermeable microchannels for microparticle synthesis from organic solvents. Another amine functional conformal coating has been designed, synthesized, and characterized. The novel alternating copolymer thin film synthesized from maleic anhydride and aminostyrene via iCVD extensively self-crosslinks after gentle heating. The annealed copolymer films display an elastic modulus exceeding 20 GPa, far greater than typical polymers (0.5-5 GPa). Moreover, the cross-linked films maintain their flexibility, neither cracking nor delaminating with repeated flexing. This achievement represents a significant advance in the fabrication of tough, durable, conformal, functional coatings. Furthermore, the highly crosslinked coating material has oxygen permeability lower than leading commercially available permeation barrier films, making it an attractive material for electronics or food industries. Also described is the utility of a new initiator, tert-butyl peroxybenzoate (TBPOB), for the iCVD synthesis. Using TBPOB instead of tert-butyl peroxide (TBPO), the rate of iCVD film growth increased by a factor of up to -8 at comparable conformality and lower the filament temperature from -250 'C to -150 'C at a comparable deposition rate. The faster deposition rates improve the economics of the iCVD process and the ability to initiate polymerizations at a much lower filament temperature reduces heat load to substrate, which is advantageous for temperature sensitive polymeric substrates or monomers that decompose at high temperatures Thesis Supervisor: Karen K. Gleason Title: Alexander and I. Michael Kasser Professor of Chemical Engineering, Associate Dean of Engineering for Research To Howard ACKNOWLEDGEMENTS Completing a PhD is truly a marathon event, and I would like to thank those who helped me complete this journey. First and foremost is my advisor, Karen Gleason, for giving me the opportunity to join the Gleason group and for her encouragement, guidance and support throughout the research project. I would not have been able to complete this journey without Karen's help. Thank you, Karen for your patience, kindness, and great advice, not only in research but also in all aspects of life. Your dedication to students and to research is very inspiring. I would like to express my sincere thanks to my committee: Professor Klavs Jensen and Professor Patrick Doyle for their invaluable guidance and support. I appreciate the discussions and the opportunities to collaborate with their graduate students, which enable me to approach my projects from different angles. I am heartily thankful to the many graduate students and post-docs I have worked with in Gleason's group. Wyatt Tenhaeff, thank you for all the kind help and great suggestions. Your insights and comments were invaluable over the years. Tyler Martin, thanks for first showing me the beauty of iCVD. Salmann Baxamusa, it is always a great pleasure to talk with you. Sreeram Vaddirajju, thanks for all the help with my troublesome pumps and the inspiring discussion. Sung Gap Im, I appreciate your help with the nanoadhesive bonding. Gozde Ozaydin-Ince, it was great to have your company at ISN! I owe a great thank you to Ayse Asatekin, whose ability to rapidly assess the worth of ideas and algorithms is really amazing. Mahriah Alf, I enjoyed sharing the reactor with you and solving the reactor problems together. Miles Barr, you are really the most original and creative person I have ever known well. Christy Petruczok, thank you for your help with the Gaussian simulation. Rong Yang, thanks for providing good company and encouragement throughout my thesis-writing period. In addition to my labmates, gratitude is also expressed to my collaborators, without whose help this work would not have been possible. Kevin Lee, thank you for providing sound advice, lots of good ideas, and good teaching of the knowledge in the microfluidics area. Ki Wan Bong, I was lucky to have the opportunity to work with you during my final stage of PhD and I am grateful to your support, understanding, and patience while we work together. Jeewoo Lim, thank you for synthesizing the amplifying fluorescentp olymers. I would also like to thank all my friends who helped me get through five years of graduate school, especially, Ying Diao. Dear diaodiao, your friendship is a treasure for me and without your help in countless ways it was impossible for me to go this far. I was so fortunate to have the greatest roommates in the world: Fei Chen, Jie Chen, and Yin Fan. I appreciate the emotional support, comraderie, entertainment, and caring they provided. I also thank some of my friends and classmates: Qing Han, Fei Liang, Ming Yang, Ben Lin, Sue Kyung Suh, David Couling, Nicholas Musolino, and Jonathan DeRocher. They each helped make my time in the PhD program more fun and interesting. I also thank the supporting staff in the department including Gwen Wilcox, Craig Abernethy, Suzanne E Maguire, Katie Lewis and Christine Preston. Finally, I am deeply indebted to my parents for providing a loving environment for me, and for their continuous support and unwavering faith in me. Mum and dad, thank you for your wholehearted support of my educational and career goals, despite of the fact that I am the only child in the family but have to move half way around the world. Thank you for teaching me the value of education and for instilling in me confidence and a drive for pursuing PhD. Most importantly, I am eternally grateful to my husband, Howard, for his constant love and strength throughout the years. He seemed to know just when I needed encouragement and without his patience, support, and understanding, I could never made it this far. Howard, you were the wind beneath my wing. Table of Content Abstract..........................................................................................................................2 Table of Content...................................................................................................... 5 List of Figures................................................................................................................8 List of Tables ............................................................................................................... 13 List of A cronym s and A bbreviations ................................................................... 14 CH A PTER O N E ......................................................................................................... 15 Introduction ................................................................................................................ 15 1.1. Background ................................................................................................... 16 1.2. Initiated Chem ical V apor D eposition (iCV D ) ............................................... 17 1.3. Functional Polymers by Vapor Deposition Techniques ............................... 19 1.4. Application of CV D Polym ers to M EM S Sealing ......................................... 24 1.5. Scope of Thesis ............................................................................................ 27 References ................................................................................................................ 30 CH A PTER TWO ........................................................................................................ 32 InitiatedC hemical Vapor Deposition ofAmine-Functionalized Thin Films' ............ 32 Abstract .................................................................................................................... 33 2.1. Introduction................................................................................................... 34 2.2. Experim ental ................................................................................................. 36 2.2.1. Film Preparation.. ...... .............. ................. ...................... 36 2.2.2. Film Characterization.. ............... . ............................ ........ 37 2.2.3. Attachm ent of CdSe/ZnS Quantum D ots................................................ 38 2.3. Results and D iscussion.................................................................................. 39 2.3.1. Film Structure Analysis .............................................................................. 39 2.3.2. Conformal Coverage ............................................................................... 42 2.3.3. Film Derivatizationw ith CdSe/ZnS Quantum Dots ........... ..... 44 2.4. Conclusion ................................................................................................... 46 A cknow ledgem ents ............................................................................................... 46 References................................................................................................................47 CHAPTER THREE .................................................................................. . ..... 48 Nanoadhesive Bonding Technique Using Amine-functional Films........................ 48 Ab stract ............................................................................................-.-..... . . ... 49 3.1. Introduction ................................................................................................. . . 50 3.2. E xperim ental ................................................................................................. 52 3.2.1. Bonding of Prototype Microfluidic Devices and Bond Strength Test ........ 52 3.2.2. Fabrication of Bioreactors Made from Polycarbonate Plasticsf or Cell gr ow th ................................................................................................................... 5 4 3.2.3. MicroparticleS ynthesis in Gas Impermeable Channels. .................. 55 3.3. Re sults and D iscussion.................................................................................. 56 3.3.1. Adhesive Bonding and Bond Strength of Sealed Microfluidic Devices...... 56 3.3.2. Hy drolytic R esistance.............. ...................................................... 57 3.3.3. Growth of E. coli in iCVD Bonded Bioreactor................... 59 3.3.4. Device fabricationf or Microparticles ynthesis ....................................... 64 3.4 .C onclusion .................................................................................................. . 68 A cknow ledgem ents.............................................................................................. 69 R eferen ces ..........................................................................................- ... ----------7-0...... CHAPTER FOUR...........................................................................71 The Design and Synthesis of Hard and Impermeable, yet Flexible, Conformal O rganic Co atings ............................................................................................. .. 71 A b stract ......................................................................... ......... --...... - --------.......7..2....... 4 .1. Introduction ................................................................................................. . . 73 4 .2. E xperim ental ................................................................................................. 76 4.3. Re sults and D iscussion.............................................................................. .. 79 4.3.1. DepositionR ate ............................. ........... 79 4.3.2. F ilm StructureA nalysis ........................................................................... 80 4.3.3. MechanicalP ropertyA nalysis ........... ................. ... 83 4.3.4. Oxygen Permeability. . ....................... ... ..... .... 90 4 .4 .C onclu sion ...................................................................................... ............ . 92 A cknow ledgem ents ............................................................................................... 92 Re ferences ............................................................................-............. .... 93 CHAPTER FIVE ......................................................................... 95 Low-temperature iCVD Process Using Tert-Butyl Peroxybenzoate as an Initiator..9 5 Ab stract ..................................................... ............ --......- . ------------........................ 96 5.1. Introduction .................................................................................. . ...... .97 5.2. Experim ental ................................................................................................... 100 5.2.1. D eposition Setup .......................................................................... 100 5.2.2. Film Characterization.. ..................................... 101 5.3. Re sults and D iscussion.................................................................................... 102 5.3.1. Deposition Kinetics ..................................... 102 5.3.2. Confirma tion of Polym erization by F TIR ................................................. 105 5.3.3. CompositionalA nalysis by XPS ............................................................... 107 5.3.4. Conforma lity A nalysis by SEM ................................................................ 109 5.4. Conclusion ...................................................................................................... 113 A cknow ledgem ents ................................................................................................ 114 References .............................................................................................................. 115 CH A PT ER SIX ......................................................................................................... 117 Conclusions. ............................................................................................................. 117 A PPEND IX A ............................................................................................................ 125 Integration of Amplified Fluorescent Polymer (AFP) Detection Schemes into M icrofluidic System s ................................................................................................ 125 References .............................................................................................................. 129 List of Figures Figure 1-1. (a) iCVD reactor scheme. (b) iCVD deposition mechanism.................. 17 Figure 2-1. Fourier transform IR (FTIR) spectra of (a) 4-aminostyrene (4-AS) monomer, (b) iCVD deposited poly(4-aminostyrene) (PAS), and (c) PAS standard from Polysciences. Asterisks (*) represent signature vinyl bonds and dotted line refers to the sp3 C -H stretching. ........................................................................................ 40 Figure 2-2. XPS survey scan for detection of the atomic concentration of oxygen, nitrogen, and carbon................................................................................................. 4 1 Figure 2-3. Step coverage as a function of aspect ratio square. The dashed line (R2>0.99) represents the linear best-fit line for the data and its slope is proportional to the sticking probability of the initiating radical. Here the three different aspect ratios for the trenches are 8.7, 5.5, and 3.4 respectively.................................................... 43 Figure 2-4. Cross-sectional SEM images films of (a) iCVD PAS, (b) PECVD PAAm, and (c) the relative thickness variation of films with respect to the trench position in (a) an d (b )......................................................................................................................4 4 Figure 2-5. Amine functional groups density comparison between iCVD PAS and PECVD PAAm. (a) photoluminescence (PL) results. Three different spots were measured for each sample. Fluorescence micrographs of (b) iCVD PAS and (c) PECVD PAAm. The images insert in the top right of (b) and (c) represent background when there is no quantum dots attached to the surface.............................................45 Figure 3-1. Adhesive bonding process. (a) Substrate cleaning by oxygen plasma for 0.5-1 min (b) iCVD deposition of Glycidyl Methacrylate (c) iCVD deposition 4- Aminostyrene (d) Adhesive layer curing at 50 'C for 24 hours. .............................. 53 Figure 3-2. Schematic of the bioreactor design. ....................................................... 54 Figure 3-3. Fabrication process of gas impermeable channels................................. 56 Figure 3-4. Hydrolytic resistance study. (a) Schematic of a PC-PDMS-PC structure used in the blister test (b) plot of the channel maximum pressure versus water soaking 8 time. Dotted line shows a markedly bond strength decrease in devices utilized PAAm- PGMA chemistry. The bond starts to degrade after 6 hours and completely fails after 18 hours. The solid line represents bond strength for devices utilized PAS-PGMA chemistry. It remains almost unaffected even after 2 weeks. .................................. 58 Figure 3-5. iCVD bonded chips for E. coli growth.................................................. 60 Figure 3-6. Growth curve for the culture experiment grown with E. coli FB 21591...61 Figure 3-7. Effect of coating thickness on the oxygen concentration for the growth of E .co li F B 2 159 1. .......................................................................................................... 62 Figure 3-8. Effect of coating thickness on the oxygen permeation coefficient of poly(glycidyl methacrylate) (PGMA) deposited PDMS membranes. ...................... 63 Figure 3-9. Organic solvent resistance. Bonded microfluidic devices with NOA81 and PDMS channels (a) before toluene flow and (b) after flowing toluene for 5 min. Bonded microfluidic devices with homogeneous NOA81 channels (c) before toluene flow and (d) after flowing toluene for 30 min. ......................................................... 65 Figure 3-10. (a) Schematic of microparticle synthesis in homogeneous NOA81 microchannels using hydrodynamic focusing lithography. (b) Synthesized microparticles from top and side views. (c) Particles with controllable height synthesized in the iCVD-bonded microfluidic device.............................................66 Figure 3-11. (a) Schematic of Ruthenium encapsulated microparticle synthesis from organic solvents. (b) Optical and fluorescence micrographs of synthesized Ruthenium encapsulated mi croparticles..................................................................................... 67 Figure 4-1. Deposition rate as a function of monomer partial pressure ratio. .......... 80 Figure 4-2. Fourier transform IR (FTIR) spectra of iCVD (a) poly(maleic anhydride) (PMa) , (b) poly(4-aminostyerene) (PAS), and (c) poly(4-aminostyerene-alt-maleic anhydride) (PA SM a)................................................................................................. 81 Figure 4-3. Measured maleic anhydride (Ma) contents and Carbon: Nitrogen ratios of the iCVD-deposited copolymers as a function of the ratio of Ma/AS flow rates.........82 Figure 4-4. Mechanical property improvement of annealed PASMa copolymer. (A) Effect of annealing time on the Young's modulus and hardness of copolymers. (B) Load-displacement curves from nanoindentation for the as-deposited and annealed cop o ly me rs....................................................................................................................84 Figure 4-5. Mechanical property comparison of as-deposited and 24-hr annealed PASMa copolymer with a wide variety of organic and inorganic materials30......85 Figure 4-6. Scratch resistance. AFM images of nanoscratches on (A) polystyrene, (B) as-deposited iCVD PASMa copolymer film, and (C) 24-hr annealed PASMa copolymer film. Nanoscratch height profiles of (D) polystyrene, (E) as-deposited iCVD PASMa copolymer film, and (F) 24-hr annealed PASMa copolymer film. All the experimental conditions in the nanoscratch experiments were kept identical. The PASMa copolymer film thickness is ~1 micron in (B), (C), (E), (F). ..................... 87 Figure 4-7. Flexibility test. Optical micrographs of as-deposited iCVD PASMa copolymer films on polycarbonate substrates after (A) 75 folds, (B) 150 folds, and (C) 200 folds. Optical micrographs of 24-hr annealed iCVD PASMa copolymer films on polycarbonate substrates after (D) 75 folds, (E) 150 folds, and (F) 200 folds. All the experimental conditions were kept identical. The PASMa copolymer film thickness is ~2 0 0 nm ......................................................................................................................... 89 Figure 4-8. Oxygen permeability measurements. (A) The effect of annealing time on the oxygen permeation coefficient of PASMa copolymer films of 200 nm thick. (B) The oxygen permeation coefficient comparison of the 24-hr annealed PASMa copolymer film with commercially available permeation barrier films31. .............. 91 Figure 5-1. Initiators and monomer used in this work..................... 101 Figure 5-2. Deposition rate as a function of filament temperature, with TBPOB and TBPO as initiators. Flow rates of monomer and initiator precursors, substrate temperature and monomer partial pressure are identical for the two sets of ex p erim en ts.................................................................................................................10 3