MICROSTRUCTURE AND RHEOLOGY OF POLYDISPERSE, CHARGED SUSPENSIONS

Nonequilibrium Brownian dynamics simulations are used to study the eff ect of polydispersity on the thermodynamics, rheology, microstructure, and shear-induced disorder-order transition in suspensions of charged colloids. Approximately 43 000 particles with 2000 different componen ts of a discretized Schulz distribution at polydispersities from 0% to 30% are simulated on a massively parallel computer. Recent advances i n the integral equation theory for polydisperse suspensions are tested and verified with respect to both structure and equilibrium mechanica l properties. The low shear rate theology for both monodisperse and po lydisperse suspensions is found to be well represented by the Ree-Eyri ng model. At higher shear rates an ordered ''string'' phase is shear i nduced for low polydispersities (< 10%). Increasing the polydispersity further (> 20%) inhibits the ordering, suggesting the existence of a critical polydispersity beyond which a colloidal suspension cannot be induced into an ordered state by shearing; The validity of a generaliz ed, nonequilibrium Stokes-Einstein relationship for polydisperse collo ids is also investigated. (C) 1996 American Institute of Physics.