Solvent-transfer assisted photolithography of high-density and high-aspect-ratio superhydrophobic micropillar arrays

An effective and facile route of solvent-transfer assisted photolithography (STAP) was explored to successfully fabricate uprightly standing high-density (HD) and high-aspect-ratio (HAR) micropillar arrays with excellent superhydrophobicity. The collapse problem that frequently occurs with the HAR micro or nano-structures was simply resolved by the combined optimization of an SU-8 UV photolithographic process that aimed to maximize the stiffness of HAR pillars and minimize the capillary effect by fully optimizing UV exposure, resist baking and the final step of rinse and drying. The SU-8 micropillar array with high density close to 29% and varied aspect ratio up to 13:1 can be fabricated in an equivalently effective but less time-consuming and simpler way compared to conventional techniques of supercritical point drying and freeze drying. As a result, the SU-8 surfaces structured with the upright standing HD and HAR micropillars created by the combined optimization of the STAP process were demonstrated to be of superhydrophobicity with a contact angle up to 162° and those pillars array with varied AR above 5:1 assumed a slightly varied level of superhydrophobicity. (paper)