Creating Super-oleophobic Surfaces

A number of surfaces encountered in nature are superhydrophobic, displaying water contact angles (WCA)> 150°, and low contact angle hysteresis. The most widely-known example of a superhydrophobic surface found in nature is the surface of the lotus leaf. It is textured with small 10-20 micron sized protruding nubs which are further covered with nanometer size epicuticular wax crystalloids.1 Numerous studies have shown that it is this combination of surface chemistry plus roughness on multiple scales – micron and nanoscale that imbues super hydrophobic character to the lotus leaf surface. The question we seek to answer is whether it is also possible through control of surface chemisty and morphology to create surfaces which show comparable levels of oil-repellency. Two distinct models, developed by Cassie2 and Wenzel,3 are commonly used to explain the effect of roughness on the apparent contact angle of a drop sitting on a surface. The Wenzel model recognizes that surface roughness increases the available surface area of the solid, which geometrically increases the contact angle for the surface according to