Structure and Dynamics in Colloid-Polymer Mixtures Out of Equilibrium

Abstract

Colloidal dispersions out of equilibrium have wide-ranging applications in science and engineering, including biotechnology, consumer products, and the chemical industry. Examples include high-throughput particle separation using microfluidic devices, the deposition of multilayer or functional coatings, and the assembly of colloidal crystals for optics and photonics. Colloidal dispersions are typically carefully engineered and often have multiple components, e.g., hard particles, polymers, and surfactants. A key challenge is to connect the microscopic properties of the colloidal dispersion to the macroscopic properties that emerge such as large-scale assembled structures or the suspension rheology. Predicting this relationship is complicated by the intimate coupling between structure and dynamics in colloidal suspensions at the microscopic level, which is the focus of this dissertation.

Massive-scale molecular simulations are applied to study the structure and dynamics of colloids, polymers, and their mixtures out of equilibrium. The simulations are accelerated by algorithms and software developed for the massively parallel architectures of graphics processing units. I first investigate the cross-stream migration of colloids in microfluidic channels. A distinct focusing into the channel center is obtained for colloids in dilute polymer solutions, but significant scatter around this focused position is observed due to conformational fluctuations in the polymer solution. I next consider the flow-induced axial dispersion of colloids in microfluidic channels. I develop a complete theoretical framework for analyzing this dispersion, finding that it is critical to consider microscopic structuring due to confinement when the colloid diameter is comparable to the channel size. Nonequilibrium structure formation in drying films is then explored. I demonstrate how mixtures of colloids and polymers vertically segregate (stratify) into layers and propose a model for this process based on dynamical density functional theory. I finally consider the evaporation-induced assembly of colloidal crystals, showing how solvent evaporation influences early stages of crystal formation but that structural rearrangements compete with the drying dynamics at later times to determine the final morphology. In all cases, hydrodynamic interactions are shown to play an essential role in determining the colloid dynamics.