Shape-recovery in organic solvents of water-responsive cellulose nanofiber actuators

In this work, we have prepared films based on cellulose nanofibers (CNFs) that mimic plant responsiveness to water by shape-changing. Film twisting was achieved by creating an asymmetrical expansion through a gradient of carboxylate groups within the CNF film thickness. We present the characterization of pristine and modified CNFs, and their swelling and mechanical performances when conditioned into films. The immersion in water and organic solvents (isopropanol, ethanol, DMSO, acetonitrile, and cyclohexane) allowed controlling the asymmetrical expansion. Hence, film twisting is triggered when immersed in water and their shape recoveries were accomplished by dipping them in organic solvents. We investigated the main physicochemical interactions between the different CNFs and solvents governing film expansion. This work leaves the door open for the design of biomimetic cellulose-based materials for soft robotics, building materials, and electronic applications.

Automated summary

Films based on cellulose nanofibers (CNFs) that imitate plant responsiveness to water by changing shape were prepared. The films twisted due to an asymmetrical expansion created by a gradient of carboxylate groups within the CNF film thickness. The swelling and mechanical performances of pristine and modified CNFs conditioned into films were investigated. Immersion in different solvents allowed controlling the asymmetrical expansion and triggering film twisting in water and shape recoveries in organic solvents. The study of physicochemical interactions between CNFs and solvents provides insights for the design of biomimetic cellulose-based materials for various applications.