Electric-field-driven contact-line dynamics of two immiscible fluids over chemically patterned surfaces in narrow confinements.

We investigate the contact-line dynamics of two immiscible fluids in a narrow fluidic confinement comprising wettability-gradient surfaces, where the bulk fluid motion is actuated by an externally applied electric field. We assume that the channel walls bear spatially uniform surface potential. Our analysis, based on the diffuse interface formalism, reveals that the contact line undergoes stick-slip motion over the chemical patches and its velocity is a strong function of the interfacial electrokinetics. We also show that the tendency of the contact line of getting pinned to the selected patches can decrease or increase with its progression along the channel, depending on the ratio of the permittivities of the two fluids. Finally, we establish the functional dependency of the time taken by the contact line to move across the patches (capillary filling time) on the combined consequences of interfacial electrochemistry and wettability patterning.