Impact of Chitosan's Degree of Deacetylation, Molecular Weight, and Crystallinity on the Photoresponsive Properties of Azobenzene-modified Films and Membranes

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 10-30mol% of the light-responsive azobenzene derivativeDuring 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.