Nonequilibrium molecular dynamics simulations of oscillatory sliding motion in a colloidal suspension system

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Abstract
In the large shear region, concentrated colloidal systems exhibit two characteristic layered structures under an oscillatory shear flow [Ackerson and Pusey, Phys. Rev. Lett. 61, 1033 (1988)]. The two structures have close packed triangular lattices stacked perpendicular to the shear rate (velocity gradient) vector but are different with the orientation of lattice vectors. The lattice is rotated by 30° or 90° at the transition point. We carried out nonequilibrium molecular dynamics simulations in a model atomic system interacting via a short range repulsive force and obtained structures corresponding well to those observed in the Ackerson-Pusey experiments. The mechanism of phase changes in this system can be explained by potential energy calculation on two sliding neighboring layers. In this model calculation, the most stable structures under oscillatory shear flows are those avoiding the overlap with particles in neighboring layers, which thereby reduce the dissipation due to shear oscillation.