Highly sensitive photoresponsive polyamide 6 nanofibrous membrane containing embedded spiropyran

Photoresponsive materials with high photoresponse sensitivity and photofatigue resistance are indispensable for applications, such as textiles and sensors fields. Herein, we synthesized photoresponsive polyamide 6 (PA6) with spiropyran (SP) as molecular component, by incorporating spiropyran-containing diisocyanate activator into anionic ring-opening polymerization of epsilon-caprolactam. To improve photosensitivity and reduce response time, the corresponding nanofibrous membranes were obtained by electrospinning. The reversibility of the isomerization of SP resulted in colored nanofibrous membrane patterns, which can be written, erased, and rewritten, using UV light and visible light. It revealed that photosensitivity of nanofibrous membranes were further improved, when appropriate polyethylene glycol was covalently embedded into PA6 segments to increase the chain flexibility. Photoresponse reversibility and photofatigue resistance displayed that UV-vis absorbance intensity of SP-embedded PA6 nanofibrous membrane decreased just 13% after 10 cycles of UV light irradiation, while its absorbance intensity in UV-vis spectra after visible light irradiation has negligible decrease. For better understanding the structure, electronic characteristics and UV-vis absorbance peak of SP-embedded PA6, theoretical calculations were also carried out. Finally, UV absorption of transparent and flexible poly(dimethyl siloxane) (PDMS)/photoresponsive nanofibers composite film was assessed. The composite film was photochromic, and possessed excellent property for blocking ultraviolet radiation.

Automated summary

Photoresponsive polyamide 6 (PA6) incorporating spiropyran (SP) was successfully synthesized and electrospun into nanofibrous membranes with improved photosensitivity. Reversibility of SP isomerization allowed for writable patterns on the nanofibrous membranes, while covalent embedding of polyethylene glycol further enhanced photosensitivity. The composite film of transparent and flexible poly(dimethyl siloxane) (PDMS) with photoresponsive nanofibers showed photochromic behavior and strong UV radiation blocking ability.