Study of Swelling Behavior of Sustainable Chitosan Nanocomposite Thin Films

Humidity sensors have attracted significant attention in recent years in both the academic and industrial field. Recently, sensors made of synthetic thermoplastic polymers and inorganic semiconductors have raised environmental concerns. Biodegradable chitosan-based nanocomposite films provide a more sustainable alternative. The protonation of NH₂ groups of chitosan increase moisture affinity. Films of 120-350nm thickness were coated on Si substrate, and rapid swelling of the thin films in humid environment was identified with visible changes in color. Film thicknesses over the relative humidity range of 45-90% increased about 50% compared to dry state; confirmed by in-situ interferometry. Addition of graphene oxide (GO) at 0.5-2wt% increased film stability due to polarity. The affinity of blended nanocomposite films towards moisture followed same trend because of the interaction of oxygen-rich GO groups and NH₂–rich groups of chitosan. This highly responsive, humidity-dependent colorimetric property of chitosan nanocomposite thin films enables potential applications as a biopolymer-based sensor.

Funding: AFOSR W911NF2010281