Gyroid-structured nanoporous chitosan from block copolymer template for UVC reflection

Abstract

Bioinspired from structural coloration of butterfly wing structure, this work aims to fabricate nanoporous chitosan for UVC reflection. By taking advantage of self-assembled polystyrene-b-polydimethylsiloxane (PS-b-PDMS) with double gyroid texture followed by hydrofluoric acid etching of PDMS block, nanoporous PS with well-defined nanochannels can be fabricated, and used as a template for templated crosslinking reaction of chitosan through a multiple pore-filling process. Well-ordered nanoporous chitosan with shifting networks in nanoscale can be successfully fabricated after removal of the PS template. With the low absorption of chitosan in the ultraviolet region and the shifting networks for opening the bandgap, it is appealing to exploit the nanonetwork chitosan as high reflective materials for UVC optical devices, as evidenced by finite-difference time-domain (FDTD) simulation and optical measurements experimentally. Gyroid-structured nanoporous chitosan is successfully fabricated by templated crosslinking reaction using nanoporous polymer as a template. A multiple pore-filling process is developed for templated synthesis to give well-ordered nanoporous chitosan. Bio-mimicking from the structural coloration of butterfly wing structure, the nanoporous chitosan with gyroid texture is highly appealing in the application of high reflective materials for UV optical devices.