Diffusion through Free Volume Redistribution
Department of Chemical and Materials Engineering
University of Alberta
Tuesday, September 3, 2019
C2-361 (Reading Room)
Diffusion in polymers, including small molecules in polymers as well as polymers in polymers, is a topic of significance to a wide variety of applications in chemical and materials engineering. Such applications encompass the removal of solvents and unreacted monomers from freshly made polymers, separation of gas mixtures using polymer membranes, drying of polymer coatings, food packaging using multi-layer plastic films, contact lens design, delivery of hydrophobic drugs and fertilizers in a controlled manner using block copolymers, to name a few. In this seminar, I will present some recent results of the aforementioned topics studied by the technique of molecular simulation, demonstrating that the free volume theory is useful for describing diffusion of small molecules in polymers. In fact, molecular simulation provides an effective means to study how do molecular structure and atomic-level interactions determine diffusivity. For diffusion in high molecular weight polymer melts, the reptation theory along with the concept of entanglement is widely accepted in the polymer literature. However, the theory does not explain what entanglements are and when and how do they come about. We do not know how to measure them directly either, as we do not know yet how to identify particular local topological features that favour entanglements. Given the inadequacy of the entanglement concept, my group is developing a free volume theory to describe the diffusion in high molecular weight polymer melts. The theory is able to account for the crossover of the chain length dependence of the centre-of-mass self-diffusion coefficient of polymer melts observed experimentally.
Phillip Choi is Professor of the Department of Chemical and Materials Engineering at the University of Alberta. He is a registered professional engineer in the province of Alberta and a Federal Court approved Expert Witness in Polymer Science and Engineering. He is also elected Fellows of the Chemical Institute of Canada and Engineering Institute of Canada. Prof. Choi received his BASc (1988) in Chemical Engineering from the University of British Columbia and his MASc (1992) and PhD (1995), both in Chemical Engineering, from the University of Waterloo. During the period of 1990 – 1995, he was a visiting scientist at Xerox Research Centre of Canada. His current research interests lie in the areas of design/development of synthetic and bio-based polymers for applications involving controlled release of small molecules and of solvent extraction of oil sands, respectively. He has authoured and co-authoured 3 book chapters, 120 referred journal publications and 1 US patent. He is also a coauthor of a textbook entitled “The Elements of Polymer Science and Engineering,” 3rd edition (2013) published by Elsevier. When Prof. Choi was a graduate student at the University of Waterloo, in 1994, he won the Teaching Assistant Award from The Sanford Fleming Foundation. He was named the McCalla Professorship in 2007 and won the Faculty of Engineering Undergraduate Teaching Award in 2008 at the University of Alberta recognizing his dedication to undergraduate education. He received a National Young Innovator Award from Petro Canada Inc. in 2001 and an international IUPAC Travel Award in 2002, respectively, recognizing his work on polymer research.
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