Wetting Behaviors of Ethanol/Water on Rough PTFE Surface

The wetting behaviors of ethanol/water solutions with different surface tensions were studied on the rough superhydrophobic polytetrafluoroetylene (PTFE) coating. Air fraction was calculated using Cassie equation, and the forces were compared. The result indicated that the ethanol/water solutions gradually filled in the multilevel structures of the PTFE coating with the decrease in the surface tension. Only the stripe structure was filled when the surface tension was greater than 28 mN·m−1. When the surface tension was less than 28 mN·m−1, the papillary structure was also filled. Because it has little contribution to the air fraction, the surface could not be wetted when the stripe structure was filled. However, the surface could be wetted by the solutions when the papillary structure, which had a considerable contribution to the air fraction, was filled.