Abstract
Wettability and evaporation of dilute sodium dodecyl sulfate (SDS) droplets on micropillar-arrayed polydimethylsiloxane (PDMS) were experimentally studied. It was found that the apparent, advancing and receding contact angles all decreased with the increase of initial SDS concentration and wettability of dilute SDS droplets depended on both SDS concentration and surface roughness. Due to the adhesion between the droplets and the micropillars, all evaporation began with constant contact radius (CCR) mode. It is more interesting that short-time spontaneous spreading was found to follow the CCR stage for dilute SDS droplets evaporating on the patterned surface with sparser micropillars, which can be attributed to the transition from the Cassie-Baxter wetting state to the Wenzel wetting state (CB-W transition). Such a transition has been experimentally observed and a theoretical model was developed to qualitatively elucidate the spontaneous spreading.
Published Version
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