Nanopore-Enhanced Drop Evaporation: when Cooler or More Saline Water Droplets Evaporate Faster

The evaporation of water droplets on surfaces is a ubiquitous phenomenon in nature and has critical importance in a broad range of technical applications. Here, we show a substantial enhancement of liquid evaporation rate when droplets are on nanoporous thin film surfaces. We also reveal how this nanopore-enhanced evaporation leads to counterintuitive phenomena: cooler or more saline water droplets evaporate faster. We find indeed that, contrary to typical evaporation behavior of sessile droplets on nonporous surfaces, the droplets placed on nanoporous thin films evaporate more rapidly when salt concentration increases or when the temperature decreases. This peculiar droplet evaporation behavior is related to the key role of the steady wetted annulus that is self-generated into the nanopore network in the drop periphery, which leads to an effectively enhanced evaporation area that controls the overall evaporation process. Our results provide the prospect of conceiving fresh scenarios in the evaporation of drops on surfaces in both relevant applications and fundamental insights.