Wettability and evaporation of dilute sodium dodecyl sulfate droplets on micropillar-arrayed non-wetting surfaces

Wettability and evaporation of dilute sodium dodecyl sulfate (SDS) droplets on micropillar-arrayed poly-dimethylsiloxane (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 be-tween 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.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The wettability and evaporation behavior of dilute sodium dodecyl sulfate (SDS) droplets on micropillar-arrayed poly-dimethylsiloxane (PDMS) surface were experimentally investigated. It was found that the contact angles of the droplets decreased with increasing initial SDS concentration, and the wettability depended on both the SDS concentration and surface roughness. The evaporation process started with a constant contact radius (CCR) mode due to the adhesion between the droplets and the micropillars. Interestingly, short-time spontaneous spreading was observed during the evaporation of dilute SDS droplets on sparser micropillar patterns, which could be attributed to the transition from Cassie-Baxter wetting state to Wenzel wetting state.