Turning over a new leaf

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The lotus leaf sets the international benchmark for the ability of its leaves to repel water, but a study published in the Journal of the Royal Society of New Zealand classified some New Zealand natives as ‘superhydrophobic’—species of hebe (Veronica albicans), Euphorbia (Euphorbia glauca) and also the rengarenga lily (Arthropodium bifurcatum).

Water droplets on leaves with rough surfaces touch only the waxy microstructures or epidermal cells sticking up from the surface, and the air pockets between them. The drops therefore can’t wet the actual surface of the leaf, and bead up even more than water drops do on a Teflon-coated frying pan. (The more tightly they bead up, the more ‘hydrophobic’ the surface.)

Leaves of plants such as kauri or flax have no prominent structures sticking out from their surfaces and so are not hydrophobic at all.

Lead scientist Geoff Willmott says that looking at superhydrophobicity in nature is valuable in the design of surfaces which need to remain clean, free of ice, or otherwise efficiently repel water.

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