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Title: The kinetics of phase transitions in polydisperse systems
Author: Williamson, John Joseph
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2013
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The study of soft matter's phase behaviour is based on thermodynamics, originally developed to describe systems i) composed of identical particles, and ii) in their final equilibrium state. However, a practical understanding requires knowledge of how real systems do (or do not) actually approach equilibrium. This is especially diffcult to achieve when, as often in soft matter, the constituents are polydisperse, i.e. comprise continuously non-identical particle species. I present a wide-ranging simulation study of phase transition kinetics in the presence of polydispersity, in the context of model colloidal systems. After briefly exploring the structural and dynamical physics of polydisperse systems, I show that fractionation (the partitioning of a polydisperse property between phases) may be enacted in the very early stages of phase separation, and highlight the qualitative sensitivity of this effect to the details of inter-particle potentials. I study the effects of metastable gas-liquid separation on crystal growth, finding a complex dependence on polydispersity which I explain with novel fractionation and local size correlation measurements. I test a theory of fractionation against experimental data in a colloid-polymer mixture with small polymers, a regime in which the widely-used Mean-Field Asakura-Oosawa (MFAO) model becomes unphysical, and find that qualitative agreement can be obtained via a simple modification of the MFAO theory. I precisely measure the composition of a diffusively-grown hard sphere crystal with small polydispersity. The results are agnostic about a prediction that diffusion in- duces nonequilibrium fractionation, but do show that equilibrium composition is not achieved: to within extremely small error bars, the crystal does not fractionate at all during growth. I examine crystal growth on an epitaxial substrate composed of dual crystal templates. Finally, I study the interdependent diffusion of particle size and concentration in a polydisperse hard sphere uid, isolating the eigenmodes implied by the BMCSL polydisperse free energy.
Supervisor: Evans, M. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available