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

The shear induced disordering transition as observed in a dilute suspe nsion of charged colloidal particles is modeled using nonequilibrium B rownian dynamics simulations. We report both real space and reciprocal space representations of the structure and dynamics of the sequence o f steady states found as the shear rate is increased. While reproducin g the observed steady-state structures at low shear rates, the simulat ed system was found to follow a different path to disorder with increa sing shear. We find that the disordering process involves the accumula tion of interstitial-vacancy defects in the shearing crystal as the sh ear rate increases. The disordering transition is also shown to exhibi t 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 coup ling of long-wavelength fluctuations with the shear flow, eventually r esults in a collective disordering similar to the process of defect-in duced amorphization in atomic solids. (C) 1995 American Institute of P hysics.