(253g) Local and Large-Scale Structure in Sheared Suspensions and Their Impact on Macroscopic Properties

We present results of a Stokesian Dynamics study of sheared Brownian suspensions, over ranges of particle volume fractions and Péclet numbers, both in two and three dimensions, with an emphasis on the relation between changes in the structure and macroscopic properties as shear thickening occurs and jamming is approached. To that end, novel (to this application) advanced measures of structure are used which enable static and dynamic investigations spanning a variety of length scales, such as the triplet distribution function and various statistical measures of particle clusters and Voronoi polygons. The triplet distribution function, widely used in liquid state theory, plays a role in theories of phase transitions of equilibrium systems and is used in the construction and validation of pair-distribution closure approximations in theoretical models; we demonstrate the connection of the triplet and pair correlations which suggests a route to understanding the many-particle structures induced by shear. The cluster statistics algorithm of Sevick et al. (J. Chem. Phys. 88(2), p. 1198, 1988) is used to identify assemblies of nearly touching particles and to generate statistics of their mean size, linear extent, and fractal dimension; note that a finite lubricating layer is always present in the simulations. The cluster-stress correlation is conveniently examined with the help of Voronoi polygons constructed around the suspended particles. The statistics of the polygon size, aspect ratio, and orientation distributions allow the interrogation of particles' nearest-neighbor environments. These elucidate the transition from well-dispersed particles to large clusters and stress chains. Some commentary is offered on the relationship of these colloidal stress chains to so-called force chains seen in dry granular media. We also demonstrate and discuss fore-aft asymmetric deviations in the average pair velocity profile that are due to the many-particle interactions in a concentrated suspension.