Robust\nand Highly Sensitive Cellulose Nanofiber-Based\nHumidity Actuators

Abstract

The\ndesign of humidity actuators with high response sensitivity\n(especially actuation time) while maintaining favorable mechanical\nproperties is important for advanced intelligent manufacturing, like\nsoft robotics and smart devices, but still remains a challenge. Here,\nwe fabricate a robust and conductive composite film-based humidity\nactuator with synergetic benefits from one-dimensional cellulose nanofibers\n(CNFs) and carbon nanotubes (CNTs) as well as two-dimensional graphene\noxide (GO) via an efficient vacuum-assisted self-assembly method.\nOwing to the excellent moisture sensitivity of CNF and GO, the hydrophobic\nCNT favoring rapid desorption of water molecules, and the unique porous\nstructure with numerous nanochannels for accelerating the water exchange\nrate, this CNF/GO/CNT composite film delivers excellent actuation\nincluding an ultrafast response/recovery (0.8/2 s), large deformation,\nand sufficient cycle stability (no detectable degradation after 1000\ncycles) in response to ambient gradient humidity. Intriguingly, the\nactuator could also achieve a superior flexibility, a good mechanical\nstrength (201 MPa), a desirable toughness (6.6 MJ/m³),\nand stable electrical conductivity. Taking advantage of these benefits,\nthe actuator is conceptually fabricated into various smart devices\nincluding mechanical grippers, crawling robotics, and humidity control\nswitches, which is expected to hold great promise toward practical\napplications.