Concentrated Colloidal Dispersions

Abstract

The rheology of dispersions often appears to be extraordinarily complex since these materials traverse all states of matter from simple Newtonian fluids to Hookean solids. Highly nonlinear viscoplastic or viscoelastic responses, with persistent time dependence, often frustrate attempts to address the mechanics without attempting to characterize the composition or understand the thermodynamics. The difficulty lies in the sensitivity of the stresses to the microstructure, which in turn depends on the interparticle forces and the deformation history.However, combining rheological measurements with other probes of the structure can permit one to anticipate the response under different conditions and, sometimes, to elucidate the relevant forces. Even better, one may learn to manipulate the composition to obtain the rheology desired for a specific process or a particular product, such as thickeners for coatings. The key lies in linking the composition, interparticle forces, and rheology. This review illustrates the current knowledge of those relationships and identifies some sources, from which the bulk of the content comes for those who wish to pursue the subject further.This brief treatment first surveys phase behavior and interparticle forces. These concepts, combined with dimensional analysis and simple ideas from statistical mechanics, motivate correlations of data for well-characterized, stable dispersions and both weakly and strongly flocculated dispersions.