Fabrication of super water-repellent surfaces by nanosphere lithography

Inspired by the water-repellent behavior of the micro- and nano-structured plant surfaces, superhydrophobic materials, with a water contact larger than 150°, have received a lot of research attentions recently. It has been suggested that contamination, oxidation and current conduction can be inhibited on such superhydrophobic surfaces, and the flow resistance in the microfluidic channels can also be reduced using super water-repellent materials. However, to fully utilize the water-repellent properties of the nanostructured surfaces, it is necessary to investigate the relationship between the nanostructure and the water repellent behavior on surfaces, and to fabricate the nanostructured surfaces with desired surface hydrophobicity. We have developed a simple approach for fabricating tunable superhydrophobic surfaces using a combination of nanosphere lithography and plasma etching. It has been found that the water contact angle on these surfaces can be systematically tuned from 132° to 168° by trimming the diameters of polystyrene nanospheres using oxygen plasma. The water contact angles measured on these surfaces can be modeled by the Cassie's formulation without any adjustable parameter.