Capillary rise in superhydrophilic rough channels

Surface tension forces enable a liquid to rise against gravity when wettable tubes or porous media are in contact with the pool of liquid. While the rise dynamics in the media of homogeneous porosity are well known, those in heterogeneous porous media still remain poorly understood. Here, we employ a vertical channel formed by two parallel plates decorated with micropillars, as a simple model of bidisperse porous media, and observe the rise dynamics of various viscous liquids. We find the bulk rise speed to be higher than that in dry smooth channels but equal to that between prewetted smooth channels. As the bulk approaches its equilibrium height, a film emerges ahead of the bulk meniscus, which is driven by the high surface energy of the microdecorated surface. The film extension grows initially like t but later like t1/2, with t being time. We construct theoretical models to predict th…