Photo-controllable contact angle hysteresis on an artificial Azo-IPN petal

This paper presents a biomimetic rose petal whose contact angle hysteresis can be reversibly tuned by photo-illumination. With azobenzene interpenetrating polymer network, the micron- and nano-scale surface structure of a rose petal was duplicated. By changing the exposure light wavelength, the surface free energy of the artificial petal was modulated between trans-to-cis azobenzene photo-isomerations. The static contact angle of the artificial petal can be tuned to range from 99.2 ± 0.9° to 140.9 ± 1.8°. The contact angle hysteresis between 50.3 ± 0.6° and >84° can be achieved. Comparing to the value measured on a real rose petal, the fabricated counterpart presents more prominent petal effect in terms of larger static contact angle and greater contact angle hysteresis.