SHEAR-INDUCED ORDERING IN SIMULATIONS OF COLLOIDAL SUSPENSIONS - OSCILLATORY SHEAR AND COMPUTATIONAL ARTIFACTS

We report on the nature of the shear induced order observed in nonequi librium Brownian dynamics simulations of particles interacting via a s creened Coulomb potential. Under steady shear, the nature of the order ed phase differs depending on the temperature. Below the equilibrium m elting temperature, the shear induced order takes the form of hexagona lly packed strings aligned along the direction of flow. Above the melt ing temperature, the liquid organizes itself into unstructured layers whose normal lies parallel to the shear gradient. We find a significan t and anisotropic system size dependence of the ordering transition un der steady shear. The critical shear rate required for ordering increa ses with increasing length of the simulation cell along the direction of flow. No such size dependence is found in oscillatory shears whose amplitude is less than half the cell length. Our results suggest that the order found in simulations under steady shear is an artefact of ps eudo-oscillations resulting from shearing through the periodic boundar y conditions. (C) 1996 American Institute of Physics.