Pattern formation in driven colloidal mixtures:: tilted driving forces and re-entrant crystal freezing

The influence of an external field actin g differently on the two constituents of a binary colloidal mixture performing Brownian dynamics is investigated by computer simulations and a simple theory. In our model. half of the particles (A particles) are pulled by an external force (F) over right arrow ((A)) while the other half (B particles) are pulled by an external force (F) over right arrow ((B)). If (F) over right arrow ((A)) and (F) over right arrow ((B)) are parallel and the field-free state is a mixed fluid. previous simulations (Dzubiella J et al 2002 Phys. Rev. E 65 021402) have shown a nonequilibrium pattern formation involving lanes of A or B particles only, which are sliding against each other in the direction of the external forces. In this paper. we generalize the situation both to nonparallel external forces and to field-free crystalline states. For nonparallel forces. lane formation is also observed but with an orientation tilted with respect to the external forces. If the field-free state is crystalline, a continuous increase of the parallel external forces yields a novel re-entrant freezing behaviour: the crystal first melts mechanically via the external force and then recrystallizes into demixed crystalline lanes sliding against each other.