Photoresponsive superhydrophobic coating for regulating boundary slippage.

A photoresponsive copolymer containing catechol and azobenzene derivatives was synthesized. The copolymer easily attached onto various substrates and showed a photoresponsive characteristic because of its catechol and azobenzene functional groups. The copolymer was successfully assembled on nanoparticles, plate mica, and rough anodized aluminum surface. The rough anodized aluminum sheet retained the Cassie-Baxter state after being modified with the copolymer. Moreover, surface adhesion can be interchanged by changing the UV exposure time. The sliding and adhesive states of water droplets were achieved by UV exposure and dark storage. Boundary slip on the rough sheet was measured using a commercial rheometer, and interchangeable slip length was also obtained after irradiation or storage. The versatile, substrate-independent approach may be significant in the development of new materials for smart fluid devices.