Structures formation in binary fluids driven through patterned microchannels: effect of hydrodynamics and arrangement of surface patterns

Through computer simulations, we examine the behavior of two partially miscible fluids, A and B, that are driven by a pressure gradient to flow through microchannels, which are decorated with A- and B-like patches. The A-like patches are preferentially wetted by the A fluid and similarly, the B-like patches are wetted by the B component. We focus on two specific arrangements of the A and B patches and investigate how a competition between the advection from the imposed flow and the preferential interactions at the patches affect the flow behavior and steady-state morphology within these channels. In the first case, a single B patch across the top and A patch across the bottom of the microchannel are shown to switch the relative orientation of the two-stream flow from vertical to essentially horizontal. When both A and B patches are placed on the top and bottom surfaces, the system exhibits a temporally periodic state, where the A and B fluids are intertwined. Estimates show that the above behavior can be observed, for instance, in viscous fluids driven through channels whose height and width are in the order of 1 μm. Both examples indicate that the introduction of chemical patches onto the walls of the microchannels can be exploited to control the flow and morphology of binary fluids in the system.