Swelling Behavior of Sustainable Chitosan/Graphene Oxide Nanocomposite Ultrathin Films*

Humidity sensors play an essential role in monitoring product quality in the manufacturing and pharmaceutical industries. Lately, the use of thermoplastic polymers and inorganic semiconductors in sensors is raising environmental concerns owing to non-degradability despite their performances. Biodegradable and renewably-sourced chitosan-based nanocomposite films provide a more sustainable alternative. Chitosan has good thermal properties and can be chemically modified by blending polar nanofillers like graphene oxide (GO), improving its mechanical properties. The oxygen-rich groups of GO and protonation of NH₂ groups of chitosan increase the affinity of these blend films towards moisture. Here, ultrathin chitosan/GO nanocomposite films of 30-500nm thickness were fabricated on Si substrate. The thin films swelled rapidly in a humid environment, with visible changes in color. Over the full relative humidity range of 95%, film thicknesses increase 50% compared to dry state, confirmed by in-situ interferometry. The absorption-desorption of moisture was fast and repeatable. This highly sensitive humidity colorimetric property of chitosan/GO nanocomposite films enable its potential as a biodegradable sensor for monitoring systems benefiting several industries.