Impact of Medium Wettability in Geometrical Valving Based on Immiscible Displacement in Porous Media

Controlling the flow and valving in microfluidic devices where external small fluctuations can trigger a cascade of unpredicted events is a challenging task in experiments. Based on concepts of capillary displacement in porous media, we design a microfluidic valve that consists of arrays of parallel triangles. Flow is allowed in one direction and prohibited in the opposite direction due to capillary effects. Previous simulations suggest a strong valving effect over a considerable range of Capillary numbers. Here, we control the wettability of the medium and study the applicability of this geometrical valve for different physical conditions experimentally. Our results show a strong effect of medium wettability on valving between water and air even at small capillary numbers. A hydrophobic medium inhibits flow over a large range of imposed pressure on the water while an extremely hydrophilic medium almost never valves. Interestingly, in the regime of intermediate wettability, we observe efficient valving over a considerable range of contact angles.