Preparation of Reversible Photoresponsive Poly(SPA-co-M MA) Films by Electrospinning: A Possible Route to Smart Materials for Regulating Wettability and Humidity

The control of surrounding humidity by porous films is an interesting aspect for improving human comfort. Especially, light triggered humidity control is of relevance because light stimulus is contactless so that reducing the impact on both materials and surroundings. In this work, reversible light responsive films with tunable wettability and the ability of regulating surrounding humidity are developed from acrylated spiropyran (SPA)-methyl methacrylate (M MA) copolymer by electrospinning. The electrospun films for regulating wettability and surrounding humidity can be reversibly manipulated by the simple switch of UV and visible light irradiation because of the unique transformation between polar ring-opened status and nonpolar ring-closed status of spiropyran units. Morphology analyses and Cassie theory are used to explain this phenomenon and it is found that surface microstructure and effective chemical composition of the film surface can both significantly influence the reversible variation range of the value of surrounding humidity and surface wettability. The results show that the ability to regulate humidity of 40 wt% poly(SPA-co-MMA) film possessing bead-on-string fiber surface structure is the best.