Self-cleaning of superhydrophobic surfaces by self-propelled jumping condensate

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 110; no. 20; pp. 7992 - 7997
• Main Authors: Wisdom, Katrina M., Watson, Jolanta A., Qu, Xiaopeng, Liu, Fangjie, Watson, Gregory S., Chen, Chuan-Hua
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 14-05-2013; National Acad Sciences
• Subjects: Adhesiveness; Animals; Cicadas; Cleaning; Condensation; Contaminants; Contamination; Gravity; Hemiptera; Hydrophobic and Hydrophilic Interactions; Hydrophobic surfaces; Imaging; Insecta; Liquids; Materials Testing; Mechanics; Microscopy, Atomic Force - methods; Models, Statistical; Nanostructures - chemistry; Physical Sciences; Stress, Mechanical; Surface Tension; Vapors; Vibration; Viscosity; Water - chemistry; Water vapor; Wettability; Wings, Animal - physiology; nanostructured interfaces; particle adhesion and removal; capillary forces; water-repellant insect wings
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1210770110

The self-cleaning function of superhydrophobic surfaces is conventionally attributed to the removal of contaminating particles by impacting or rolling water droplets, which implies the action of external forces such as gravity. Here, we demonstrate a unique self-cleaning mechanism whereby the contaminated superhydrophobic surface is exposed to condensing water vapor, and the contaminants are autonomously removed by the self-propelled jumping motion of the resulting liquid condensate, which partially covers or fully encloses the contaminating particles. The jumping motion off the superhydrophobic surface is powered by the surface energy released upon coalescence of the condensed water phase around the contaminants. The jumping-condensate mechanism is shown to spontaneously clean superhydrophobic cicada wings, where the contaminating particles cannot be removed by gravity, wing vibration, or wind flow. Our findings offer insights for the development of self-cleaning materials.