THE SHEAR-INDUCED DISORDERING TRANSITION IN A COLLOIDAL CRYSTAL - NONEQUILIBRIUM BROWNIAN DYNAMIC SIMULATIONS

The shear induced disordering transition as observed in a dilute suspension of charged colloidal particles is modeled using nonequilibrium Brownian dynamics simulations. We report both real space and reciprocal space representations of the structure and dynamics of the sequence of steady states found as the shear rate is increased. While reproducing the observed steady-state structures at low shear rates, the simulated system was found to follow a different path to disorder with increasing shear. We find that the disordering process involves the accumulation of interstitial-vacancy defects in the shearing crystal as the shear rate increases. The disordering transition is also shown to exhibit an anisotropic dependence on system size. These two observations are combined in a new picture of the shear induced disordering transition. In this model a nonequilibrium defect density, generated by the coupling of long-wavelength fluctuations with the shear flow, eventually results in a collective disordering similar to the process of defect-induced amorphization in atomic solids. (C) 1995 American Institute of Physics.