Chitosan/Polyvinyl Alcohol-Based Direction-Controlled Photo-Humidity Dual Responsive Membrane

Photoresponsive materials based on azobenzene (Azo) and its derivatives have attracted wide attention because the cis-trans isomerization of Azo under illumination often leads to changes in shape, color, size, polarity, and so on; it has great application potential in soft robot, actuator, sensor, and other fields. In this paper, by using evaporation-induced self-assembly method, taking advantage of the hydrogen bonding among chitosan (CS), polyvinyl alcohol (PVA) and Azo, and by polishing and grinding the surface of the adopted silicon film mold in advance to form grooves, the Azo/CS/PVA film with a certain degree of oriented aggregation convex surface was prepared. The film has good deformation characteristics of dual response of light and humidity. Also, it has excellent light response direction controllability under UV light, sunlight, and LED illumination. By studying the structure, morphology, photo-stimulus response behavior, humidity-photo response behavior, and mechanical properties of the films, it is found that when the Azo content reaches 10% wt, the response speed is the fastest and the response deformation is the largest. The result shows that under the irradiation of summer sunlight (sunny day), the film can reach 144°directional bending within 55 s. Moreover, the film has excellent humidity response performance, which can absorb sweat in the fingertips, deform quickly, and recover quickly after leaving fingers. The film with an Azo content of 10% wt has a fast humidity response speed, and the maximum bending angle is 140°.The designed simple sunlight response driver can lift a heavy object five times heavier than itself to a certain height, and realize the effective conversion from light energy to mechanical energy. This work effectively broadens the application range of bio-based environmentally friendly materials and has guiding significance for the development and design of multi-stimulus response intelligent materials. The light response directional control method is simple and practical. It is of great significance for the effective utilization of solar energy.