Dual wettability on diarylethene microcrystalline surface mimicking a termite wing

The termite wing has a specific property of wetting in contact with a water droplet: it adsorbs water mist, whereas larger water droplets are bounced on the surface. This is owing to the survival strategy of termites. Here, we reproduce the termite wing’s dual wettability by a photoinduced crystal growth technique. Upon UV irradiation to a microcrystalline surface of a mixture of two diarylethenes, two types of needle-shaped crystals of distinctly different sizes are observed to grow. The surface shows behavior akin to the termite wing’s dual wettability. The bouncing ability of a water droplet is attributed to the smaller-sized needle crystals, whereas the adhesive property is owing to the larger-sized ones, explaining the microstructures of the termite wing. Considering dissipation energy and adhesion energy, the bouncing ability and dual wettability can be explained theoretically. The surface could potentially be used in water harvesting applications. Molecular photoswitches can imbue materials with striking properties. Here a mixture of two photoswitchable diarylethenes forms both water-retentive and water-repellent crystals, causing small water drops to be retained while larger drops are repelled, akin to the behaviour of termite wings.