Suppressing the Universal Occurrence of Microscopic Liquid Residues on Super-Liquid-Repellent Surfaces.

Super-liquid-repellent (SLR) surfaces based on surface micro/nanotextures are generally regarded as "non-wettable", though careful examination shows that residual microdroplets remain atop surface textures upon drop shedding-off. Despite its great importance, the origin of microscopic liquid residues remains poorly explored, and how to suppress residue formation is an open question. Herein, on the basis of high-speed microscopic imaging and numerical simulations, we resolve the fast formation dynamics of liquid residues on micropillared SLR surfaces and show that the competition of contact line receding on micropillars and the pinch-off of microcapillary bridges governs residue formation. The local receding angle can temporarily reduce to be drastically lower than the intrinsic one accompanying occurrence of accelerated contact line receding, inevitably leading to capillary bridge pinch-off and residue formation. We further show a liquid-like coating can delay capillary bridge pinch-off and reduce residue volume on SLR surfaces by more than 80% compared to those with conventional perfluoroalkylsilane coatings.