Simulation Studies of Nonequilibrium Collective Phenomena in Colloids

We use Brownian dynamics simulations of colloidal systems to explore new nonequilibrium collective effects. Colloids driven over a symmetric flashing periodic substrate undergo a ratcheting behavior which can be used to fractionate different particle species. The addition of nondriven colloids can increase the drift velocity of the driven colloids due to collective interactions. We show that colloids in optical trap lattices can be used to create an artificial spin ice system which shows a rich variety of ice rule and other orderings. Our study of an interstitial point defect in a two-dimensional colloidal crystal shows that it is more mobile than a vacancy defect due to the more two-dimensional character of the diffusion. We also demonstrate that a bidisperse, phase segregated colloid system can be mixed efficiently in the absence of temperature by driving the colloids over a random substrate and inducing plastic flow.