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Don't get wet! The UV irradiation of a photochromic diarylethene microcrystalline film and its subsequent temperature treatment leads to the formation of water-repellant surfaces with different microstrucures. Depending on the microstructure, a water droplet will either roll off the surface (lotus effect) or stay pinned to it (petal effect; see picture).
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Uchida et al. (2010) studied this question.
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