Analysis of nonequilibrium structures of shearing colloidal suspensions.

The two-particle correlation function is related to the structure factor by an integral transform and serves as an important connection between suspension microstructure, scattering experiments, and macroscopic properties. The nonequilibrium structure factor for a shearing colloidal suspension of spherical particles is expanded in spherical harmonics. Through this expansion, we demonstrate formal relationships between the experimentally accessible static structure factor, bulk stresses, and optical dichroism and birefringence, demonstrating that a limited number of expansion terms are required to characterize the suspension rheology. Low shear limiting theories are expressed in terms of this expansion, demonstrating the utility of the expansion for comparison of experimental measurements of nonequilibrium structure factors to theoretical predictions. Although flow birefringence and the thermodynamic shear stress are calculated as weighted integrals over the nonequilibrium microstructure in the low shear limit, no simple stress-optical coefficient is found. The expansion is proposed as a consistent methodology for analysis of experimental data and presentation of theoretical predictions, providing a means of interpreting rheo-optical data. [ABSTRACT FROM AUTHOR]