Recyclable Chitosan-Modified Cellulose Fiber Porous\nStructure for Sensitive and Robust Moisture-Driven Actuators and Automatic\nCooling Textiles

Moisture-driven\nactuators featuring programmable stimuli-responsiveness\nand a rapid response have garnered substantial research attention.\nCellulose-based actuators face challenges, including prolonged and\nunstable responsiveness, along with inadequate interfacial bonding.\nHerein, we developed a bilayer structured moisture actuator by integrating\nmultiscale cellulose fibers with chitosan. The protonated chitosan\nforms strong electrostatic attractions with negatively charged cellulose\nnanofibrils (CNF), achieving a robust interfacial interaction. Leveraging\nthe hierarchically porous structure and varying hygroscopicity of\nmicrofibrillated cellulose (MFC) and CNF, the film establishes an\neffective wettability gradient, enabling a stable and rapid moisture\nactuation performance. The bilayer film exhibits large deformation\ntoward moisture with a bending angle of 60°, a short response\ntime of 12 s, good stability over 50 wetting and drying cycles, and\npromising recyclability. Harnessing these advantageous properties,\nthe bilayer film was demonstrated for its applications in automatic\ncooling textiles, contactless electrical switches, and artificial\nmoisture-activated muscles, showing great potential for practical\nuse.