Kinetics of capillary wetting in nanoporous films in the presence of surface evaporation

A liquid in contact with a nanoporous Au film forms a halo of constant width around the droplet. Due to the large surface area-to-volume ratio, one would expect either complete wetting or rejection of the liquid. Instead, a stable halo width is observed, depending on pore size, void fraction, film thickness, and the liquid. This is due to competition between capillary flow and evaporation through the surface of the nanoporous film. A theory is presented that predicts the halo width from the film geometry and liquid properties. Without adjustable parameters, the theory is in good agreement with experimental results.