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

The influence of an external field acting 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 (A) while the other half (B particles) are pulled by an external force F (B). If F (A) and F (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. 1