Hydrochromic and photoswitchable polyacrylic nanofibers containing spiropyran in eco-friendly ink-free rewriteable sheets with responsivity to humidity

Nowadays, reversible colorimetric devices and probes based on photoswitchable polymeric matrices are of considerable interest in variety of applications. Herein, we represent the design and preparation of hydrochromic and photoresponsive poly (methyl methacrylate-co-hydroxyethyl methacrylate) (P(MMA-co-HEMA)) and poly (methyl methacrylate-co-butyl acrylate) (P(MMA-co-BA)) through a facile emulsion polymerization doped with hydroxyl functionalized spiropyran (SPOH). Then, the obtained photoactive copolymers solutions were either electrospun to nanofibers (MH/SP@NF and MB/SP@NF ) or drop casted to films (MH/SP@F and MB/SP@F) in order to investigate their performances. The participation of HEMA and BA in copolymerization with MMA was assessed by ATR-FTIR analysis. SEM images revealed bead-less and smooth nanofibers of MH/SP@NF and MB/SP@NF with average diameter of 116 and 188 nm, respectively. UV-vis spectroscopy results demonstrated 3-5 folds increment in SP to MC switchability for MB/SP@NF and MH/SP@NF with respect to photoresponse time and about 2 folds increment in humidity- and hydro-responsivity in comparison with their corresponding films. The hydrochromic and humidity responsive behavior of the photoswitchable nanofibers and films demonstrated that P(MMA-co-HEMA) substrate showed remarkable color change and higher chromatic efficiency relative to P (MMA-co-BA) one. Enhanced photofatigue resistance and erasable behavior of MH/SP@NF for optical patterning and rewriteable sheets were conducted by alternating UV (365 nm) and visible illuminations and repeating "write-erase" cycles. The prepared stimuli-responsive MH/SP@NF sample with reasonable photosensitivity and hydro-reversibility exhibited an improved potentiality in ink-free rewriteable aqua-sensitive sheets and fabrics, humidity sensors and optical patterning.