Pattern formation in colloidal mixtures under external driving fields

摘要

The influence of an external field acting differently on the two constituentsof a binary colloidal mixture performing Brownian dynamics is investigated bycomputer simulations and a simple theory. In our model, one half of theparticles ($A$-particles) are pulled by an external force ${\vec F}^{(A)}$while the other half of them ($B$-particles) are pulled by an external force${\vec F}^{(B)}$. If ${\vec F}^{(A)}$ and ${\vec F}^{(B)}$ are parallel and thefield-free state is a mixed fluid, previous simulations (J. Dzubiella et al,Phys. Rev. E {\bf 65} 021402 (2002)) have shown a nonequilibrium patternformation involving lanes of $A$ or $B$ particles only which are slidingagainst each other in the direction of the external forces. In this paper, wegeneralize the situation both to non-parallel external forces and to field-freecrystalline states. For non-parallel forces, lane formation is also observedbut with an orientation {\it tilted} with respect to the external forces. Ifthe field-free state is crystalline, a continuous increase of the parallelexternal forces yields a novel {\it reentrant freezing} behavior: the crystalfirst melts mechanically via the external force and then recrystallizes intodemixed crystalline lanes sliding against each other.