Vapor Swelling of Polymer Brushes Compared to Nongrafted Films

Response to Comment on "Vapor Lubrication for Reducing Water and Ice Adhesion on Poly(dimethylsiloxane) Brushes": Organic Vapors Influence Water Contact Angles on Hydrophobic Surfaces

Fast removal of water drops from solid surfaces is important in many applications such as on solar panels in rain, in heat transfer, and for water collection. Recently, a reduction in lateral adhesion of water drops on poly(dimethylsiloxane) (PDMS) brush surfaces after exposure to various organic vapors was reported. It was attributed to the physisorption of vapor and swelling of the PDMS brushes. However, it was later pointed out that a change in the interfacial energies by vapor adsorption could also have caused low drop adhesion. To find out how strongly each effect contributes, contact angles of water drops on three hydrophobic surfaces in different vapors are measured. In water-soluble vapors, a substantial decrease is observed in contact angles. This decrease can indeed be explained by a vapor-induced change in the interfacial tensions. The very low contact angle hysteresis on PDMS surfaces in saturated n-hexane and toluene vapor cannot be explained by a change in interfacial tensions. The observation supports the hypothesis that these vapors adsorb into the PDMS and form a lubricating layer. It is hoped that these findings help to solve fundamental problems and contribute to applications, such as anti-icing, heat transfer, and water collection.