<p>Many biological surfaces (e.g. bird feathers, insect wings, and plant leaves) are super-hydrophobic with physical morphology at different scales (a mix of micro-bumps and a nano wax layer). However, it is not well understood how a raindrop impacts natural super-hydrophobic surfaces, and its significance of biological functions. In this talk, we will present how a high-speed raindrop impacts and spreads on various biological surfaces. First, we observed that a spreading drop at a high speed can generate wrinkled pattern (including shock-like waves) on a spreading liquid in the presence of surface morphology at the micro scale. Also, the shock-like pattern has an opening&nbsp;angle, which can predicted by a balance between a liquid spreading speed and a Taylor-Culick speed.&nbsp;Next, the spreading drop is suddenly ruptured by nucleating and growing holes followed by the shock waves. The hole nucleation occurs only on top of a micro-bump and the holes&nbsp;expand&nbsp;their&nbsp;radius rapidly. Having such fast growing holes on a spreading drop&nbsp;leads to a decrease in contact time more than 50 %. As a result, heat and momentum transfers could be reduced by high-speed raindrops, which may lower the hypothermia risk of animals or less affect the stability of insect flights.&nbsp;</p>

Drop Fragmentation on Biological Surfaces

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

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