SIMULATIONS OF SHEAR-INDUCED MELTING AND ORDERING

We describe the effect of shear on the solid-liquid phase boundary of particles that interact via a screened Coulomb potential. Both fcc and bcc phases shear through layer-over-layer sliding. As the shear rate gamma increases from zero, the degree of disorder in the layers increases and the stacking sequence changes. A first-order shear-melting transition occurs if the temperature is greater than about half of the equilibrium melting temperature T(m)eq. Near T(m)eq the transition rate is proportional to T(m)eq - T. As gamma increases further, shear becomes an ordering influence and a reentrant solid phase is observed. Dimensionless plots of the nonequilibrium phase diagram and of the shear stress versus strain rate show considerable universality and are in excellent agreement with experiments on charge-stabilized colloidal suspensions.