Surface Termination Engineering of 2D Titanium Carbides for Light-Activated Soft Robotics Applications

The transition metal carbide (TMC) Ti3C2Tx exhibits exceptional electrical conductivity, photothermal conversion, and mechanical flexibility. The latter two properties are useful for creating coatings that convert light into heat, which can enable photothermal actuation. However, the performance of such actuators utilizing Ti3C2Tx is constrained by unfavorable surface terminations (e.g., -F) formed during traditional wet acid etching synthesis, which compromise both electrical conductivity and photothermal efficiency. This study introduces a novel plasma-enabled atomic layer etching (plasma-ALE) approach to precisely engineer the surface termination of Ti3C2Tx post-synthesis. The one-step ALE process transforms the surface chemistry from fluorine-dominated to oxygen-dominated terminations, resulting in an 80% increase in electrical conductivity and significantly enhanced photothermal conversion efficiency. By incorporating actuation-enhancing cellulose nanofibrils, ALE-treated Ti3C2Tx/cellulose actuators demonstrate dramatic increases in both bending angle and force under near-infrared light illumination, outperforming other 2D material-based actuators. Various actuator manufacturing techniques, including vacuum filtration and aerosol jet printing, have been employed, demonstrating plasma-ALE’s compatibility with multi-scale pattern designs ranging from millimeter to centimeter dimensions. Furthermore, plasma-ALE treatment facilitates actuators capable of grasping and locomotion. This work paves the way for advanced surface engineering of TMCs and their integration into multifunctional soft robotic systems.