Humidity-stimulated film actuator with dual-responsive of bending deformation and discoloration

Flexible actuator can timely sense the changes of the external environment and respond accordingly. However, most intelligent response systems relied on the input of external electrical energy and can only trigger a single response, which cannot adapt to the changing environment. Here, the transparent actuating film TiO2/PVA-co-PE/SA was obtained by simple high-pressure spraying and immersion methods. Due to the excellent hygroscopicity of sodium alginate, the TiO2/PVA-co-PE/SA composite film can undergo rapid and reversible actuating deformation under external moisture stimulation. Meanwhile, the addition of titania-mica pearlescent pigment made the surface color of the composite film can be freely switched with the change of bending angle. Moreover, the actuating deformation and color variation showed excellent stability, and the maximum bending angle of the composite film can be maintained about 140°during ten consecutive cycles of moisture stimulation. The actuating film with synchronous change of shape and color has great significance in the research field of smart home and bionic system.