Variable wettability control of a polymer surface by selective ultrasonic imprinting and hydrophobic coating

Surface wettability is the ability of a liquid to maintain contact with a solid surface, and there have been many studies aimed at controlling surface wettability for development of functional surfaces. In this study, an approach to control surface wettability is proposed by differentiating surface energy of polycarbonate in specified regions, using a combination of two surface treatments: (i) micropattern replication using selective ultrasonic imprinting and (ii) hydrophobic coating using organic silane. In both treatments, profiled masks were used to reduce surface energy in target regions where semi-hydrophobic polycarbonate surfaces were changed to hydrophobic states. Various combinations of selective ultrasonic imprinting and hydrophobic coating were investigated in terms of changes in surface wettability, by measuring contact angle (CA) behaviors on the developed surfaces. By controlling such changes, the surface wettability of regions on a single polycarbonate surface could be differentiated, allowing semi-hydrophobic (CA 87.8°), hydrophobic (CA 114.8°) and superhydrophobic (CA 155.6°) states to coexist. This high CA difference (>60°) on a single surface was then applied to enhance water-repellent characteristics so that the surface wettability could be controlled effectively. Mechanical durability of the developed hybrid surface was also discussed by investigating its CA behavior after surface abrasion.