Polymer Brush Surfaces Showing Superhydrophobicity and Air-Bubble Repellency in a Variety of Organic Liquids

Silicon (Si) substrates were modified with polyalkyl methacrylate brushes having different alkyl chain lengths (C-n, where n = 1, 4, 8, and 18) using ARGET-ATRP at ambient temperature without purging the reaction solution of oxygen. The dynamic hydrophobicity of these polymer brush-covered Si surfaces when submerged in a variety of organic solvents (1-butanol, dichloromethane, toluene, n-hexane) depended markedly on the alkyl chain length and to a lesser extent polymer solubility. Long-chain poly(stearyl methacrylate) brushes (C-n = 18) submerged in toluene showed excellent water-repellant properties, having large advancing/receding contact angles (CAs) of 169 degrees/168 degrees with negligible CA hysteresis (1 degrees). Whereas polymer brushes with short alkyl-chain (C-n <= 4) had significantly worse water drop mobility because of small CAs (as low as 125 degrees/55 degrees) and large CA hysteresis (up to 70 degrees). However, such poor dynamic dewetting behavior of these surfaces was found to significantly improve when water drops impacted onto the surfaces at moderate velocities. Under these conditions, all brush surfaces were able to expel water drops from their surface. In addition, our brush surfaces were also highly repellant toward air bubbles under all conditions, irrespective of C-n or polymer solubility. These excellent surface properties were found to be vastly superior to the performance of conventional perfluoroalkylsilane-derived surfaces.