MXene-based solvent-responsive actuators with a polymer-intercalated gradient structure

Actuators based on electrically conductive and hydrophilic two-dimensional (2D) Ti₃C₂T _<i>X</i> MXene are of interest for fast and specific responses in demanding environments, such as chemical production. Herein, Ti₃C₂T _<i>X</i> -based solvent-responsive bilayer actuators were developed, featuring a gradient polymer-intercalation structure in the active layer. These actuators were assembled using negatively charged pristine Ti₃C₂T _<i>X</i> nanosheets as the passive layer and positively charged polymer-tethered Ti₃C₂T _<i>X</i> as the active layer. 2D wide-angle X-ray scattering and simulations related the gradient polymer intercalated microstructure in the polymer/MXene composite active layer to the counterintuitive actuation behavior. The bending of the bilayer films in solvent vapor is triggered by the gradient polymer-intercalation and the differing diffusion rate of solvent molecules through the MX and MX-polymer layers of the bilayer actuator. With their ease of fabrication, remote light-control capabilities, and excellent actuation performance, the Ti₃C₂T _<i>X</i> -based bilayer actuators reported here may find applications in areas such as sensors for monitoring chemical production, infrared camouflage, smart switches, and excavators in toxic solvent environments.