Using theory to predict phase behaviour in liquids, copolymer melts, and ultrathin polymer films.

摘要

Thermodynamics, and the classic balance between entropy and enthalpy, provides a proverbial zoo of exotic phase behaviour that chemists can harness to create new materials out of simple liquids and polymers. The diversity of self-assembling materials in use today is a reflection of how important an understanding of phase behaviour is, particularly from a theoretical perspective. Models of the underlying physics in these materials often serve as a guide for how new (undiscovered) materials can be created.;In Part I of this thesis, a theoretical model is developed to predict the glass transition of a promising new class of copolymers by understanding the self-assembly of microscopic structures in the sample. Self-consistent field theory for copolymers is used to examine the microscopic phase behaviour of copolymer melts, complemented by the development of theoretical models for the copolymers' phase behaviour in hypothetical limits. Further study is also performed on the behaviour of isolated copolymers in homopolymer melts, yielding a more complete picture of their phase behaviour. By understanding microscopic structure in a copolymer melt, excellent quantitative predictions for the glass transition are achieved that can be directly compared with experiment.;In Part II, attention is turned to examining the role of free volume and mobility in the glass transition of fluids and polymers. A kinetic model of free volume is developed that exhibits the iconic physical characteristics of the glass transition, including dynamic heterogeneity and sharp growth in relaxation lifetime. The model draws on observations of particle dynamics and free volume in supercooled fluids, particularly the role that free volume appears to have in propagating mobility over long ranges in a supercooled fluid. After applying the model to bulk systems, fluctuations in mobility and free volume near interfaces in fluid films and bilayers are studied. Consistency between the simulations results, and experiments on fluid films and bilayers, lends key physical insight into why such systems have phase behaviour that deviates so markedly from bulk.