Impact of chitosan's degree of deacetylation, molecular weight, and crystallinity on the photoresponsive properties of azobenzene-modified films and membranes

Abstract

A profound understanding of how the degree of deacetylation (DDA), degree of polymerization (DP) and photoswitch concentration impact the photomodulation of properties of chitosan (CS)-based responsive materials can serve as a framework for future applications. Herein, we report responsive thin-films manufactured from chitosans with DDAs ranging from 70–94% and DPs ranging from 170–3380, incorporating 10–30 mol% of the light-responsive azobenzene derivative sodium-4-[(4-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)phenyl)diazenyl]-benzenesulfonate (TEGABS). During UV irradiation of the 10–30% TEGABS|CS thin-films, e.g. a significant increase in the indentation modulus of 10 ± 5% is observed. UV illumination leads to a decrease in water vapor permeability (WVP), which is reduced by up to 81 ± 17% compared with that of the native state. We demonstrate that TEGABS up to 10% remains as a solid-solution in CS films with differing amounts of H-aggregates depending on the DDA and DP. TEGABS at concentrations >10% in CS leads to phase separation of TEGABS crystallites with a diameter of 21 ± 8 nm. To conclude, photothermal heating by UV irradiation and the resulting water evaporation are identified as the primary driving force for the variation in mechanical properties and WVP, with photoisomerization acting as a subordinate factor. These findings provide a new pathway for the design of polysaccharide-based water vapor permeable photoresponsive membranes.