Gradient Assembly Approach for Fabricating MXene-Based Dual-Responsive Soft Actuators

Soft actuators based on bilayer–multilayer structures are highly promising for the development of soft robotics. However, their long-term operational stability is often undermined by poor interlayer adhesion between different component materials. Herein, instead of adopting traditional bilayer/multilayer structures, we developed a gradient assembly approach for MXene and poly(methyl methacrylate) (PMMA) nanospheres to prepare robust humidity/light dual-responsive actuators. The gradient distribution of PMMA nanospheres along the normal direction of the MXene film yields an asymmetric structure with one side composed primarily of MXene nanosheets and the other side enriched with PMMA nanospheres. Benefiting from the asymmetric hygroscopic swelling and thermal expansion behaviors of the two sides, the composite film demonstrates reversible and rapid dual-responsive bending deformation along with outstanding long-term stability. Remarkably, the actuator exhibits a large bending angle of up to 345° under humidity stimulation and 235° under light irradiation, with fast response/recovery times of 45 ± 0.78/46 ± 0.66 s for humidity actuation and 30 ± 0.88/43 ± 0.74 s for light actuation. Moreover, it maintains excellent stability without performance degradation after 1000 cyclic actuations under both stimuli. Based on its controllable dual-response behavior, we prepared a petal mimetic actuator, a bidirectional smart switch, and a smart gripper for humidity–light synergistic manipulation, providing a design concept for soft robotics.