Structure, slow dynamics, kinetic arrest, and massively reconfigurable assembly in colloidal suspensions.

摘要

Colloidal suspensions offer the level of control necessary to assemble and form novel equilibrium, and non-equilibrium states. The realm of colloidal suspensions is vast and ripe with opportunities for synthesizing new materials possessing superlative physical characteristics. In this thesis we focus on colloidal liquids and the diverse non-equilibrium soft solids they can form, and how quenched disorder can be used to drive equilibrium assembly. These fundamental science topics are highly relevant for materials science and engineering applications.;Chapters 2 through 5 focus predominantly on slow dynamics, kinetic arrest and nonequilibrium soft solid properties and their unique applications. In Chapter 2 we explore the subtle interplay between colloidal liquid-gas macrophase separation, percolation, kinetic arrest, and space spanning gelation of short ranged attractive spherical and non-spherical colloids. We address the recent claim that space spanning gelation is solely a product of spinodal decomposition. Our key finding is that the kinetic gel line does not scale with either interactions or particle shape in the same manner as the spinodal and percolation boundaries suggesting highly non-universal behavior. In Chapter 3 we develop and apply a statistical dynamical theory for dense isotropic sphere-rod mixtures as a function of attraction strength, aspect ratio, and composition. Up to seven transiently localized phases are predicted and dynamical complexity increases with rod aspect ratio. The elastic shear modulus and absolute yield stress are predicted to undergo order of magnitude variation upon crossing non-equilibrium phase boundaries. In Chapters 4 and 5 we develop a new, non-replica based approach to treat the thermodynamics and structure of hard sphere glasses in 3 dimensions and greater. Novel predictions emerge for the glass transition and jamming densities and excellent agreement with recent simulations in elevated dimensions (above 3) is presented. In three dimensions we also explicitly probe the glass pair structure upon approach to jamming. Multiple distinctive features of jamming are recovered and the results are compared to recent replica theory approaches. With our advanced 3D hard sphere structure, we quantitatively test the Non-linear Langevin equation (NLE) theory of activated dynamics in the ultra-dense regime. At low to moderate density, relaxation times are in agreement with simulation and experiment. In the highly over-compressed regime though, NLE theory appears to miss some longer ranged correlations required to correctly capture the relaxation time growth. Calculations of the linear elastic shear modulus and absolute yield stress for nearly jammed packings are in good agreement with recent experiments on colloidal suspensions.;Chapters 6 and 7 focus exclusively on equilibrium fluid structure. In particular, we explore the possibility of using of a quench disordered large mesh gel composed of long rigid rod polymers, to provide a tool to mediate the structure and thermodynamics of colloidal suspensions. We employ the Replicated Reference Interaction Site Model approach to study a model quenched fiber gel immersed in a spherical colloid fluid. The theory predicts a sharp wetting-like transition with increasing colloid-fiber attractions accompanied by strong thermodynamic and colloid packing changes. By increasing the colloid-colloid attractions at constant colloid-fiber interactions, a surprising state of maximum adsorption is predicted. This phenomenon suggests a strategy for avoiding macrophase separation and achieving a new state characterized by large, but controlled, density fluctuations. The possibility of exploiting these phenomena to create assemblies that can be reversibly switched between electrically conductive and insulating states is explored.