PATTERNING ELASTOMER, THERMOPLASTICS AND SHAPE MEMORY MATERIAL BY UVO LITHOGRAPHY AND SOFT LITHOGRAPHY A Dissertation Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy Ying Chen January, 2017 i PATTERNING ELASTOMER, THERMOPLASTICS AND SHAPE MEMORY MATERIAL BY UVO LITHOGRAPHY AND SOFT LITHOGRAPHY Ying Chen Dissertation Approved: Accepted: ______________________ _______________________ Advisor Department Chair Dr. Alamgir Karim Dr. Sadhan C. Jana ______________________ _______________________ Committee Member Dean of the College Dr. Abraham Joy Dr. Eric J. Amis ______________________ _______________________ Committee Member Dean of the Graduate School Dr. Kevin A. Cavicchi Dr. Chand Midha ______________________ _______________________ Committee Member Date Dr. Xiong Gong ______________________ Committee Member Dr. Jutta Luettmer-Strathmann ii ABSTRACT Micro/nano patterning and structures, especially hierarchical structures have attracted great research interest in the past few decades, because these structures exhibit unique properties like tunable adhesion and wetting. Especially, micro/nano patterning is of great interest for semiconductor, micro/nano fluidics, optical and photonic devices applications. Traditional methods used for the fabrication of hierarchical structures typically involve the formation of complex patterned features through multistep lithography processes. These methods usually require expensive equipments and specialty reagents, so that the low-cost fabrication of well-controlled micro-nano patterns for diverse potential applications remains a challenge. We demonstrated a versatile and inexpensive method for controlling the surface relief structure of polymer films over large areas through a two-step imprinting process. First, nanoscale patterns were formed by nanoimprinting elastomer (PDMS) films with a pattern on a DVD disk. Micron-scale patterns were then superimposed on the nanoimprinted PDMS films by exposing them to ultraviolet radiation in oxygen (UVO) through a photomask. UVO exposure leads to a conversion and densification of PDMS to SiOx, leading to micron height relief features that follow a linear scaling relation with pattern dimension. Further, the pattern scopes are shown to collapse into a master curve by iii normalized feature values. Interestingly, these relief structures preserve the nanoscale features. In this dissertation, the influence of the self-limiting PDMS densification, walls stress at the boundary of micro depression, PDMS thickness, modulus and UVO exposure energy is studied in control of the micro depression scale. The method fidelity was evaluated in coarse-grained molecular dynamics simulations and confirmed experimentally. In the second part of this study, this simple two-step imprinting process involving both nanoimprinting and UV radiation, is studied for pattern transfer demonstration of the dimension adjustable micro-nano hierarchically structures not only on elastomer films, self-assembled monolayer and nanoparticles but also by imprinting onto thermoplastic polymer films. The patterning of thermoplastic polymer films is achieved through capillary force lithography (CFL). Fundamental study of CFL is conducted to understand the influence of film thickness and annealing process. Another two forms of soft lithography examined here include replica molding, and microcontact printing. Thus, these generated patterns are successfully extended to self-assembled monolayer and nano particles, which enlightens the further potential applications of the proposed patterning method. Finally, Shape memory compounds based on mixtures of an ionomer with a FA are used to develop shape memory or shape morphing surfaces with micro- or nano-scale features. Three different FAs, zinc stearate (ZnSt), stearic acid (SA) or lauric acid (LA) are mixed with Zn salt of sulfonated EPDM, respectively, to act as the temporary networks. As with the bulk shape memory compounds based on the ionomer/FA design, the switching temperature for micro- and nano-scale surface pattern recovery can be easily tuned by simply changing the FA used in the composition. The shape memory recovery efficiency iv of the micro and nano scaled surface topography is compared with bulk materials. The recovery behavior for the surface nanopattern, however, had lower efficiency than micropattern scale and bulk shape memory of the same material, which may be due to the effects of the excess surface energy on the dynamics of the surface patterns or creep of the temporary or permanent networks due to the high stress used to deform the nano-scale grating pattern and produce the temporary crosshatched pattern. v ACKNOWLEDGEMENTS For the past five years of studying at The University of Akron, I have received generous help from a lot of people, and this dissertation benefits so much from their kind help. I am grateful to meeting so many nice persons and worked with them, they have very big influences not only on my career but how I think about life and myself. With this project, my advisor Dr. Karim was a tremendous source of insight and practicality. I would like to express my special appreciation to him: Dr. Karim. I am also grateful to my committee members, Dr. Xiong Gong, Dr. Kevin Cavicchi, Dr. Abraham Joy, Dr. Jutta Luettmer-Strathmann for their critical review and helpful suggestions. Special thanks to all current group members and alumni of the Karim Research Group, especially for Dr. Manish Kulkarni and Dr. Diya Bandyopadhyay, due to their kind help for all of suggestions in starting and developing projects. I am extremely grateful for that. Outside the committee, my sincere thanks go to Dr. Jack Douglas, from NISR, Dr. Robert Weiss, Dr. Matthew L. Becker and Dr. Andrey V. Dobrynin, from Polymer Department for their collaborations, discussion, advices, and help during my research. It has been delighted to collaborate with them during the past five years. vi I would also like to thank Dr. Larry Rhodes at Schneller, Inc. I spent great four months doing an internship under his management. He provided me with the great opportunity to work in an industrial environment and guided me to the industry of semiconductor. I also want to thank students in the Department of Polymer Science and Engineering, Zhiyang Zhao, Zilu Wang and Changhuai Ye, for collaborations and helps throughout my research. They have been really helpful for past years, and I am very grateful for their kindness and friendship. The most special thanks go to my best family, my husband, mom, dad and brother. Your love and unconditional support is the most important thing in my life. vii CONTENTS 1 Introduction .......................................................................................... 1 2 Background .......................................................................................... 5 2.1 UV Lithography ............................................................................... 5 2.2 Soft Lithography ............................................................................ 10 Replica Molding ....................................................................... 12 Microcontact Printing ................................................................ 16 Capillary Force Lithography ...................................................... 20 2.3 Shape memory behavior.................................................................. 25 3 Methodology of a novel UVo Lithography for a dimension controlled micro- nano hierarchical patterning. ................................................................... 37 3.1 Materials ....................................................................................... 39 3.2 Experimental methods .................................................................... 39 viii 3.3 Micro-nano hierarchical patterns and parameters influencing the efficiency of UVO Lithography ........................................................................... 42 Chemistry of PDMS under UVO exposure .................................. 42 Micro-nano hierarchical pattern .................................................. 45 Parameters influencing the process of UVO induced PDMS depression ............................................................................................... 49 Simulation of the nano patterning process ................................... 55 3.4 Summary ....................................................................................... 61 4 Investigating the application of the prepared micron-nano hierarchical mold for Soft Lithography ................................................................................... 62 4.1 Materials ....................................................................................... 63 4.2 Experimental methods .................................................................... 63 Pattern transfer – Replica Molding ............................................. 63 Pattern transfer – Microcontact Printing ...................................... 64 Pattern transfer - Capillary Force Lithography ............................. 65 4.3 Micro-nano patterning through replica molding ................................. 66 ix 4.4 Micro-nano patterning microcontact imprinting ................................. 69 4.5 Defects analysis and elimination via a process optimized Capillary Force Lithography ...................................................................................................