Lotus effect uncovered
Bharat Bhushan and his team at Ohio State University, US, have been working hard to get to the bottom of nature’s most famous superhydrophobic surface - the lotus leaf. Its self-cleaning properties often hit the headlines, but the low friction material is also ideal for reducing drag flow in nanochannels.
SEM images of the leaf reveal micro-sized asperities covered with “nanobumps” that are thought to be due to the dendritic growth of wax. Bushan pointed out that the dual length scale structure allows air molecules to become trapped against the leaf when liquid rolls over the surface, enhancing the water repellent property of the material.
The team is using its analysis to come up with a synthetic version of the wonder material and has started making patterned PMMA structures coated with fluorinated silane to test various designs.
“Sharp edged asperities will pin droplets, which is bad news for fluid flow”, Bushan explained. “Ideally, you would like to have round-tipped asperities.”
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