Statics and dynamics of colloidal suspensions with attractive interactions

An understanding of the static and dynamic properties of colloidal suspensions is important to the formulation of engineering models for the design and optimization of chemical processes involving colloidal-sized particulates. When the suspended particles interact via strong attractions this understanding is largely guided by phenomenology with little theoretical basis. The goal of this dissertation is to develop improved simple liquid theories for predicting the suspension statics and to explore the applicability of a rigorous suspension theory for predicting the suspension dynamics. For this purpose, AOT/H{dollar}sb2{dollar}O/decane inverse microemulsions are used as a prototypical system for studying the effects of attractive interactions on system properties.; These inverse microemulsions show an unexplained viscosity maximum with increased swelling of the droplets. To explain this phenomenon, the system is treated as a colloidal suspension of particles interacting via an attractive square-well potential. Dilution viscometry and small-angle neutron scattering are used to probe the droplet interaction. The dilute viscosity of the square-well colloidal fluid is calculated exactly and "thermodynamic self-consistency" is imposed on the integral equation theory for the square-well fluid. These calculations are used to extract the parameters of the square-well potential from the experiments, demonstrating that the viscosity maximum is caused by increased inter-droplet attractions. A molecular mechanism is proposed, whereby disorder at the surfactant/water interface leads to increased overlap between surfactant tails and a stronger attraction.; The generalized hydrodynamics theory is explored as a route to predicting the suspension dynamics and also percolation. As a consequence of the attractive interactions, particles form clusters that can mediate charge and stress across the sample. This causes large changes in conductivity and viscosity near the percolation threshold, at which a sample-spanning cluster is formed. A phenomenological dynamic percolation criterion is proposed as the inflection point of the concentration-dependent long-time self-diffusivity. Comparison with large-scale Brownian dynamics simulations shows that this theoretical framework is a potentially useful tool for analyzing the role of colloidal attractions on the suspension properties, including rheological and percolative behavior.