Stimuli-Responsive Polymer Nanotube Arrays by KHEK-KHIANG CHIA Bachelor of Science in Engineering, Chemical Engineering University of Michigan, Ann Arbor, MI, 2005 Masters of Science in Chemical Engineering Practice Massachusetts Institute of Technology, Cambridge, MA, 2008 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 © Massachusetts Institute of Technology, 2011. All rights reserved. Signature of Author:______________________________________________________________ Department of Chemical Engineering May 19th, 2011 Certified by:____________________________________________________________________ Robert E. Cohen St. Laurent Professor of Chemical Engineering Thesis Co-Advisor Certified by:____________________________________________________________________ Michael F. Rubner TDK Professor of Materials Science and Engineering Thesis Co-Advisor Accepted by:____________________________________________________________________ William M. Deen Professor of Chemical Engineering Chairman, Committee for Graduate Students 2 Stimuli-Responsive Polymer Nanotube Arrays by KHEK-KHIANG CHIA Submitted to the Department of Chemical Engineering On May 19th, 2011 in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Engineering Abstract Nanotube arrays, composed of materials such as carbon, titania, and zinc oxide, have shown potential as conductors, energy conversion devices, actuators, and adhesives. Such nanoscale constructs are particularly novel for their high area-to-volume and length-to-diameter aspect ratios that lead to physical and chemical properties more interesting than their bulk counterparts. However, the stimuli-responsiveness of nanotube arrays has seldom been explored, mostly due to the inertness of the materials typically utilized to create them. Here I introduce a new concept of designing and synthesizing surface-bound stimuli- responsive polymer nanotubes with dynamic mechanical properties. Polyelectrolyte multilayers (PEMs) composed of poly(allylamine hydrochloride) and poly(acrylic acid) were chosen as the nanotube building blocks for their ability to undergo pH-triggered swelling-deswelling transitions. The swelling behavior was first demonstrated in the in situ synthesis of gold nanoparticles in the PEM; upon suitable post-assembly treatment, the PEM undergoes substantial molecular rearrangements that generate free amine groups available for gold salt binding. Characterization of the size and distribution of the gold nanoparticles as a function of assembly condition and post-assembly treatment, and in situ ellipsometry thickness measurement of the PEM film during the swelling transition provided further insights into the swelling behavior. These studies ultimately led to the design and synthesis of reversibly swellable PEM nanotube arrays via layer-by-layer assembly on porous templates. The template-based approach allows straightforward control over the length, diameter, orientation and lateral arrangement of the resultant tube array, which can be challenging with other synthesis methods. Activation of the swelling transition resulted in dramatic changes in the length and diameter of the tube arrays as characterized in situ via confocal laser scanning microscopy, and in the effective modulus of the nanotube arrays as measured by AFM-based nanoindentation. Parallel to experimental work, finite element analysis of simulated indentation on the nanotube arrays showed deformation mechanisms and a discontinuous stress-and-strain field different than that of a flat film. Template-based nanotube synthesis is further applied to the assembly of nanotubes with thermal- and magnetic-responsiveness, as well as incorporating cell-receptor-interacting biopolymers. Thesis Supervisors: Robert E. Cohen, St. Laurent Professor of Chemical Engineering Michael F. Rubner, TDK Professor of Materials Science and Engineering 3 Acknowledgments My advisors, Prof. Robert Cohen and Prof. Michael Rubner, have been influential in my academic and personal growth. Their enthusiasm in scientific research and dedication to teaching throughout the years showed me the lifelong fulfillment of being an educator. Like sunshine, my advisors effortlessly cheer me up when I show up at their door with a gloomy face; I always tell people how lucky I am to never have to leave their office in tears. I still vividly remember the day I shared the news to Prof. Cohen that I am going to music school after graduation; to my pleasant surprise, he was extremely happy and supportive of my decision. When he came to the premiere of my choral piece, my friends were envious that not only my advisor was committed in developing my scientific research skills, he is clearly also very compassionate about my other interests and career goals. Over the years, music classes complemented my scientific work impeccably – both providing me an intellectual and fulfilling learning experience at MIT. My classes and lessons led to tremendous growth in my musical skills and ultimately to the preparation of a portfolio for graduate school applications; I am therefore indebted to both of my advisors, who believe in high quality and well-rounded education, for giving me the academic freedom to pursue the first formal music education in my life. I would like to thank my thesis committee, Prof. Paula Hammond and Prof. Francesco Stellacci for their helpful discussions in shaping my thesis over the years. I had the wonderful opportunity to collaborate with some faculty and students in the IRG team: Lin Han, Lifeng Wang, Ilke Kalcioglu, Daniel Schimdt, Irene Chen, Prof. Christine Ortiz, Prof. Mary Boyce and Prof. Krystyn Van Vliet. I thank Wui Siew Tan and Jonathan Gilbert for always being engaging in our collaborative projects, and Erin Goodwin and Philip Schlenoff for their contribution to my thesis as summer visiting researchers. I am proud to be a member of the Cohen and Rubner groups for how intellectual yet communal and friendly we are. I thank Daeyeon Lee, Adam Nolte, Ryan Bennett, Andy Miller, Hiroomi Shimomura, Albert Swiston, Pinar Kurt, Jonathan DeRocher, Yi Du, Adam Mueler, Shreerang Chhatre, Siddarth and Hyomin Lee for creating this enjoyable working environment. Erik Williamson and Grinia Nogueira, my officemates in 13-5126, made me look forward to come to work every day for lunch. The music department has become my second base when I needed to run away from failed experiments. I am touched by Prof. Peter Child, Dr. Fred Harris, Prof. Ellen Harris, Prof. Keeril Makan, Dr. William Cutter and Dr. Charles Shadle, for their guidance, mentorship and support over my music education in the past five years. I specially thank Prof. Child and Prof. Makan in developing my musical creativity and personal growth as a composer, even in dealing with insecurities with my own work. I am incredibly grateful for Dr. Cutter’s commission of my first piece that was performed in public, Awaiting Spring, and the MIT Chamber Chorus for their dedicated performance of the piece. Since the conception of this piece, I had come to know some 4 of the greatest singers and friends at MIT: Tina Tallon, Paulina Silwa, Jiahao Chen, Adrianna Tam and Karen Lee. I also had an amazing five years of playing with the MIT Wind Ensemble under Dr. Frederick Harris. With a mentor role in the ensemble, I constantly dissuade the undergrads from drinking during our concert after-party. Greg Durett, Sarah Abraham, Katie Silberstein, Marta Lynne, Simone Ovsey, Emily Jackson, Emily Su, Shannon Taylor, Andrew Eckel and Rachel Clary: I will always remember the serious conversations we have, ranging from mountain fishing trips to bad romance to get-lucky jeans. and carbs. Like Sex and the City, my life outside of MIT was made fabulous by three BFFs - Daniel Trahan, Andrew Guerra and Bradley Niesner – whom I had regular gossip lunches with. Our Sunday brunches at Paramount after a night out at the H.O.B, C.C. or Paradise reminded me of how klassy we are. I thank my ChemE friends whom I had known since our first years for helping me through the classes and quals - Stephanie Piecewicz, Huan Zheng, Christopher Govern, Amy Chan, Mike Harper, Jen Seto, Erin Bell, Dan Schmidt, Vicki Dydek, Wayne Blaylock and Kevin Fowler. I also thank my friends Simon Choong, Fadi Kanaan, Jacob Farwell, Joe Hawley and Michael Lowenthal for making Boston felt like home. My family has been incredibly supportive throughout my life. I am very fortunate to have parents who support my education and career goals unconditionally, even when I decided to pursue graduate education in music after my Ph.D. in Chemical Engineering. Thank you all for giving me a wonderful time at MIT and in Boston for the past six years. I would not have made it through without you. 5 Table of Contents Chapter 1 Introduction ...................................................................................... 16 Motivation ................................................................................................................................. 16 Membrane-Based Approach for Tube Array Synthesis ............................................................ 19 Porous Membranes as Sacrificial Templates ............................................................................ 20 Layer-by-Layer Assembly .........................................................................................................