Hydrophobic and self-cleaning coatings

The effects of nano and micro roughness as well as the chemical composition of surface treatments on hydrophobicity and self-cleaning properties of the coated surfaces were studied theoretically and experimentally. Accordingly, relationships were derived between the interfacial adhesion strength of the liquid drop to a polymer surface of a given composition, the mass of the drop, the measured contact angles, and the sliding angle. To verify the proposed model various hydrophobic coatings having different surface nano and micro roughness were prepared using polycarbonate (PC) as a substrate. The surface treatment was based on fluoroalkylsilane. Roughness was introduced by means of Silica (micro) and polyhedral oligomeric silsesquioxane (POSS; nano) using a double morphology topography mimicking the Lotus leaf. In the case of optimal compositions and processing conditions, transparent ultra-hydrophobic characteristics were obtained. In these cases the contact angle was close to 1800 and the sliding angle was below 5 degrees. These novel ultra-hydrophobic surface coatings and the associated model could be used to develop and design surfaces for a variety of applications such as self-cleaning glazing, repellent surfaces for threats from biochemicals, and anti-icing of surfaces. Copyright (c) 2007 John Wiley & Sons, Ltd.