Pulsating flow driven alteration in moving contact-line dynamics on surfaces with patterned wettability gradients

The contact line dynamics over surfaces patterned with wettability gradients under pulsating flow condition are of essential importance in application areas ranging from the design of smart and effective microfluidic devices to the understanding of blood flow dynamics in narrow conduits. In the present study, we probe the capillary filling dynamics in a pulsatile flow environment, in an effort to explore the underlying flow physics. Presenting the results of frequency assisted contact line motion of two immiscible fluids over surfaces patterned with wettability gradients, we show how the interfacial dynamics are affected by the interplay of both the surface characteristics and flow pulsation. Our results reveal that the competition between two control parameters, the frequency and the amplitude of the imposed flow pulsation, may effectively be tuned to control the capillary filling dynamics significantly. The study, we present here, also suggests that by suitably tuning the control parameters, it is possible to control the capillary residence time over engineered locations which may, in turn, facilitate improved mixing and/or design of chemically active reaction stations.