Flexible and Robust Superomniphobic Surfaces Created by Localized Photofluidization of Azopolymer Pillars

Springtails, insects which breathe through their skins, possess mushroom-shaped nanostructures. As doubly re-entrant geometry in the mushroom head enhances the resistance against liquid invasion, the springtails have robust, liquid-free omniphobic skins. Although omniphobic surfaces are promising for various applications, it remains an important challenge to mimic the structural feature of springtails. This paper presents a pragmatic method to create doubly re-entrant nanostructures and robust superomniphobic surfaces by exploiting localized photofluidization of azopolymers. Irradiation of circularly polarized light reconfigures azopolymer micropillars to have a mushroom-like head with a doubly re-entrant nanogeometry through protrusion and inward bending of polymer film from the top edge. The light-driven reconfigured micropillars facilitate the pining of triple line as the springtails do. In particular, the unique geometry exhibits superomniphobicity even for liquids whose equilibrium contact angles are almost zero in the presence of a practical level of external pressure. In addition, the simple fabrication process is highly reproducible, scalable, and compatible with various substrate materials including flexible polymeric film. Our results suggest that our photofluidization technology will provide a practical route to develop robust superomniphobic surfaces.