Underwater Superoleophobic Surface Based on Silica Hierarchical Cylinder Arrays with a Low Aspect Ratio

A superantiwetting surface based on low-aspect-ratio hierarchical cylinder arrays (HCAs) was successfully obtained on a silica substrate by colloidal lithography with photolithography. Colloidal lithography is a technique involving transfer of a pattern to a substrate by etching or exposure to a radiation source through a mask composed of a packed colloidal crystal, while photolithography is utilized by which a pattern is transferred photographically to a photoresist-coated substrate, and the substrate is subsequently etched. The surface provides an alternative approach to apply aligned micro-nano integrated structures with a relatively low aspect ratio in superantiwetting. The obtained HCAs successfully integrated micro- and nanoscale structures into one system, and the physical structure of the HCAs can be tuned by modulating the fabrication approach. Using a postmodification process, the underwater-oil wetting behavior of cylinder-array based surfaces can be easily modulated from the superoleophobic state (an oil contact angle (OCA) of 161°) to oleophilic state (an OCA of 19°). Moreover, the underwater-oil wettability can be reversibly transformed from the superoleophobic state (an OCA of approximately 153°) into the oleophilic state (an OCA of approximately 31°) by grafting stimuli-responsive polymer (PNIPAAm) brushes onto this specific hierarchical structure. Due to the temperature-responsive property, modifying the surface with PNIPAAm provides a possibility to control the oil wettability (repellent or sticky) by temperature, which will benefit the use of HCAs in oil-water separation and other application fields.