Robust and Highly Sensitive Cellulose Nanofiber-Based Humidity Actuators

The design of humidity actuators with high response sensitivity (especially actuation time) while maintaining favorable mechanical properties is important for advanced intelligent manufacturing, like soft robotics and smart devices, but still remains a challenge. Here, we fabricate a robust and conductive composite film-based humidity actuator with synergetic benefits from one-dimensional cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) as well as two-dimensional graphene oxide (GO) via an efficient vacuum-assisted self-assembly method. Owing to the excellent moisture sensitivity of CNF and GO, the hydrophobic CNT favoring rapid desorption of water molecules, and the unique porous structure with numerous nanochannels for accelerating the water exchange rate, this CNF/GO/CNT composite film delivers excellent actuation including an ultrafast response/recovery (0.8/2 s), large deformation, and sufficient cycle stability (no detectable degradation after 1000 cycles) in response to ambient gradient humidity. Intriguingly, the actuator could also achieve a superior flexibility, a good mechanical strength (201 MPa), a desirable toughness (6.6 MJ/m3), and stable electrical conductivity. Taking advantage of these benefits, the actuator is conceptually fabricated into various smart devices including mechanical grippers, crawling robotics, and humidity control switches, which is expected to hold great promise toward practical applications.研发兼具高响应灵敏度（尤以响应时长为甚）与优异力学性能的湿度驱动器，对于软体机器人、智能设备等先进智能制造领域至关重要，但目前仍是一项挑战。本文通过高效真空辅助自组装法，制备得到一种兼具协同增效特性的坚固导电复合薄膜基湿度驱动器，其组分包含一维纤维素纳米纤维（cellulose nanofibers, CNFs）、碳纳米管（carbon nanotubes, CNTs）与二维氧化石墨烯（graphene oxide, GO）。 得益于CNFs与GO优异的湿敏特性、可加速水分子快速脱附的疏水CNTs，以及具备大量纳米通道以提升水分子交换速率的独特多孔结构，该CNF/GO/CNT复合薄膜在环境梯度湿度刺激下展现出优异的驱动性能：超快的响应/恢复时长（0.8秒/2秒）、大形变以及充足的循环稳定性（1000次循环后未检测到性能衰减）。 值得注意的是，该驱动器同时具备优异的柔韧性、良好的力学强度（201 MPa）、理想的韧性（6.6 MJ/m³）与稳定的导电性能。基于上述优势，本研究已概念性地将该驱动器制备为机械夹具、爬行机器人、湿度控制开关等多款智能设备，预计其在实际应用中具备广阔前景。