Water vapor responsiveness of chitosan: An experimental and simulation analysis.

Stimuli-responsive polymers have gained significant research interest in recent years owing to their potential applications in diverse areas. Here, we present a study on the actuation characteristics of chitosan-based free-standing films that exhibit full reversibility and repeatability in response to water vapor exposure. The effect of pH of the water and the degree of cross-linking of the chitosan films on the actuation performance is studied.

Penetrant-Induced Glass-like Transition in Thin Chitosan Films.

We present the water vapor-induced swelling and the emergence of a penetrant-induced glass-like transition in the substrate-supported glassy chitosan thin films. The time evolution of the film thickness under different levels of relative humidity conditions is measured in real-time using a spectroscopic ellipsometer equipped with a humidity cell. In a dry film, the network of chitosan chains is in a glassy state, and upon exposure to water vapor, initially, the film swells by Fickian diffusion of water molecules, which triggers the structural relaxations of the chains.

Rapid Moisture-Responsive Silk Fibroin Actuators.

We report the unique actuation characteristics of moisture-driven, fully reversible soft biopolymer films fabricated from silk. The instantaneous actuation is driven by the water vapor induced stress gradient generated across the thickness of the film, and it possesses subsecond response and actuation times. The excellent durability and consistent performance of the film without any noticeable fatigue are established by subjecting it to more than a thousand continuous actuation cycles.