Phase separation in highly asymmetric mixtures: From charged biopolymers to binary hard disks

In this dissertation I present my research into the phase behavior of multicomponent soft matter mixtures. This research has entailed the use of a wide variety of computational techniques, to disentangle and understand the complex behavior of systems with large disparities in the size and charge of the components. More specifically, I study the phenomenon of polyelectrolyte condensation, the conformations of flexible block polyampholytes, and the phase behavior of binary mixtures of hard disks.;In Chapter 2 I examine the biologically important complexation of F-actin, an anionic polyelectrolyte, and lysozyme, a cationic globular protein. F-actin is a rod-like molecule that assembles into a compact bundle in the presence of lysozyme. I use simulations to elucidate the distribution of lysozyme within the bundle, and to evaluate the stability of the bundle under various conditions. Chapter 3 presents a detailed analysis of a more generic model for polyelectrolyte condensation. I use this model to reconcile several experimental observations, and to predict a novel bundle structure for linear condensing agents.;In Chapter 4 I study the effect of multivalent salt on the conformations of a block polyampholyte, and I also present an analysis of the dependence of block polyampholyte conformations on the degree of polymerization and on the charge distribution.;Finally, Chapter 5 treats the phase behavior of both additive and non-additive binary hard disk fluid mixtures, for very large size asymmetries. Using a systematic extrapolation in the non-additivity parameter I have been able to resolve the long-standing issue of fluid-fluid phase separation in the additive system.