SHEAR MELTING OF COLLOIDS - A NONEQUILIBRIUM PHASE-DIAGRAM

Experiments show that charge-stabilized colloidal suspensions form crystals which can melt by applied shear stress. We present a molecular-dynamics simulation study of shear melting in colloids. The non-equilibrium phase diagram is calculated for a volume fraction which has an equilibrium fcc structure. The mechanism for flow in the sheared solid is found to be planes sliding over planes. We find that weak equilibrium solids (high added salt) shear melt, but strong equilibrium solids do not. Instead, shear produces a crossover to a new solid structure. This appears in the phase diagram as a reentrant solid phase. Results for shear stress and phase diagram are consistent with existing experiments.