Effect of Dew Condensation on the Wettability of Rough Hydrophobic Surfaces Coated with Two Different Silanes

Dew condensation effects on the wettability of rough and smooth coatings of two fluoroalkylsilanes (FAS3 and FAS17) were investigated by controlling the temperature. Contact angles of the coatings decreased concomitantly with decreasing surface temperature. Inflection points in the temperature dependence of contact angles were observed at the dew point. They were attributable to the change of the interfacial free energy of the solid-gas interface by water adsorption. The contact angle decrease suggested a mode transition from Cassie to Wenzel on the rough surface, and resulted from the surface wettability change and the increase of the condensation amount of water. The contact angle change by increasing temperature from -6 degrees C revealed that the Wenzel mode is more stable than Cassie's mode.