Wetting and evaporation of dilute sodium dodecyl sulfate droplets on micropillar-arrayed non-wetting surfaces under a direct current electric field

The wetting and evaporation of dilute sodium dodecyl sulfate (SDS) droplets on micropillar-arrayed polydimethylsiloxane (PDMS) surfaces under a direct current (DC) electric field were experimentally studied. It was found that both the advancing and receding contact angles decreased with increasing SDS concentration and voltage had an influence on these angles. The wetting transition from the Cassie–Baxter state to the Wenzel one (CB-W wetting transition) was observed during the wetting and evaporation of SDS aqueous droplets with a relatively low initial SDS concentration on the micropillar-arrayed PDMS surfaces under a DC electric field. For the case of electrowetting, the critical voltage for the occurrence of CB-W wetting transition was found to decrease with the increase in initial SDS concentration. For the case of droplet evaporation, the CB-W wetting transition was observed to occur earlier with the increase in the initial SDS concentration when the voltage was fixed and similar phenomenon was also found with the increase in voltage when the initial SDS concentration was kept unchanged. Finally, a theoretical model was set up to qualitatively elucidate the CB-W wetting transition.