Recently, we have shown, that low molecular weight chitosan with the azobenzene derivative TEGABS shows photomodulation of the mechanical properties and photoactuation.[1] Herein, we present a procedure to manufacture several UV-light-responsive chitosan films with different degree of deacetylation (DD, 70-95%) and polymerization (DP, 200-3500) by incorporating the azobenzene derivative Methoxy diethylene glycol azobenzene sulfonate (TEGABS). The films are investigated by Powder X-ray diffraction (PXRD), UV-VIS spectroscopy, Raman spectroscopy, FTIR spectroscopy and nanoindentation. With increasing DD at near constant DP and increasing amount of TEGABS the films show a decrease in efficiency of photoisomerization (EZ) of TEGABS and in the half-life of thermal relaxation after UV irradiation. This behavior is related to an increasing phase separation: Starting with solid-solutions of TEGABS in the chitosan matrix (low DP and low DD) TEGABS precipitates into nanocrystals with increasing DD and DP, which compromises the responsive properties. The films not only show an increase of stiffness and hardness while irradiated with UV light, they also show a light-induced removal of residual moisture. The TEGABS/Chitosan films were fabricated into membranes to test water vapor permeabilities with and without UV irradiation. The water vapor permeability decreases during irradiation with UV light. we show the potential of biogenic polysaccharides in the design of humidifying membranes with a light-adjustable permeability by DP and DD.[2]

[1] N. von Seggern, N. Oehlsen, I. Moudrakovski, L. Stegbauer, Small 2023, n/a, 2308939.

[2] The authors gratefully acknowledge the Carl Zeiss Stiftung (Perspectives project ChitinFluid, project P2019-02-004) and Fonds der Chemischen Industrie (Fellowship to L.S. and N.O.) for generous financial support, the core facility SRF Advanced Materials Innovation and Characterization (AMICA) at the University of Stuttgart for the support and assistance and Samantha Waechter for the support in conducting experiments and sample preparation.