Structure and Dynamics of Star-Polymer/Polymer Nanocomposites

Abstract

Star polymers represent the case where linear polymers are attached to a central core particle. The molecular weight of a star-polymer can be varied by altering the number of arms and/or the length of each arm. Star-polymers are similar to polymer-tethered nanoparticles in the limit where the nanoparticle size is very small. We study how the properties of pure-polymer melts are altered by adding a small fraction of star-polymers.We study star-polymer/polymer composites by employing molecular dynamics simulations. We quantify how a small fraction of added star-polymer changes the dynamics and glass transition of a bulk pure-polymer material and how these changes depend on the number and length of star arms, as well as intra-star molecular interactions. We find star-polymers are most effective at altering the polymer dynamics when the stars adopt expanded "fluffy" conformations, which can be affected by topology and the internal star interactions. We rationalize these effects by relating the glass transition temperatures to high-temperature activation energy parameters. We extend these observations to the case of ultra-thin composite films, where the stars potentially preferentially segregate to one of the interfaces, which can enhance or diminish the changes that arise from confinement in the film geometry. Thus, star-polymers appear to be a promising route to rationally control property changes in bulk and confined polymer materials. I'm not sure words exist for the degree of appreciation I have for those who have made this thesis possible. My friend and mentor Professor Francis W. Starr never stopped pushing me beyond what I thought I was capable of. His unending patience, encouragement, and support has shaped who I am today. Thanks to him, I have become a better writer, science communicator, and critical thinker. So if you're reading this man, you have really made a huge impact in my life as a role model. I'd also like to thank two professors who have ignited a flame in my soul. Professor Blümel's continued enthusiasm while teaching Quantum Mechanics II made me rediscover my love for physics. Professor Personick's expertise in nanotechnology and guidance in applying for graduate school solidified my choice to pursue a career in science. Both of you made it possible for me to attend graduate school. Thank you to my readers, Professor Paily and Brian. I have had the pleasure of taking courses with the both of you. Professor Paily was my first physics professor at Wesleyan. Your kindness and enthusiasm is recognized by all physics majors I know. Brian, your yearly earth rants are events I don't want to miss. Your support and insights also motivated me to pursue graduate school. I'd also like to give a big shout out to Starr Lab. Thank you Hongjia Z, Rakib H, Tom MS, and Tom A for the deep philosophical conversations, moments shared in Chicago, insights, and friendship. I look forward to continuing work with you all in the future. Thank you Jinpeng Fan for early guidance. Thank you to my dearest friends and housema...