  In this paper, we depict interfacial electro-thermo-chemical-hydrodynamics of
two immiscible fluids in a microchannel with substrates patterned by ribs. The
motion of the binary fluids is set by an alternating current electrothermal
(ACET) mechanism. Our investigations, based on free-energy-based phase field
formalism, reveal that the capillary filling dynamics and the contact line
motion are strong functions of the wetting characteristics and geometric
parameters of the patterned ribs. Modulation of these parameters alters the
surface energy over the rib surface, which, in turn, facilitates the
interaction between interfacial tension and driving electrothermal forces. The
competition between two forces may speed up or slow down the fluid-fluid-solid
contact line motion over the rib surface. At the edges of the ribs, the
interface can halt for a sufficiently long time owing to contact line pinning.
Alteration in positions of the rib between the electrode pairs changes the
electric field strength and thereby bulk ACET forces across the contact line.
Further, by suitable arrangement of the ribs, various intricate shapes of the
liquid front can be achieved over a short distance, which can have significant
implications in the morphological control of microscale flows.
