Superwettability with antithetic states: fluid repellency in immiscible liquids

Abstract

A surface repels a fluid in an immiscible liquid when it stabilizes the former at a non-wetted Cassie state and the latter at a fully-wetted Wenzel state. Chemically, this occurs only when the former non-wets and the latter wets the surface. Here, we report the removal of the long-standing chemical constraints by harmonizing the antithetic states with rationally-designed anisotropic surface topology so that the super-repellency can appear in virtually any two-fluid system. Inspired by the 3D multi-layered structures of diatom frustules, our surface texture design introduces the required direction-dependent energetic barriers to create and stabilize the Cassie and Wenzel states, respectively. The multi-layered cage structure is found to be the best in achieving under-liquid repellency. We fabricate the required surface architecture by the microfluidics method and show experimentally its super-repellency of gas, water, and oils in all six types of fluid–liquid systems with a single micro-cage surface. Such super-repellent surfaces would be important in various fields that involve multiple fluids and anisotropic solid–liquid interactions.