(649d) Surface-Agnostic Highly Stretchable and Bendable Conductive Mxene/Polymer Multilayers for Sensing Applications

Stretchable, bendable, and foldable conductive coatings are crucial for wearable electronics and biometric sensors. Such coatings should maintain functionality while simultaneously interfacing with different types of surfaces undergoing mechanical deformation. MXene sheets as conductive 2D nanomaterials are promising for this purpose, but it is still extremely difficult to form surface-agnostic MXene coatings that can withstand extreme mechanical deformation. Herein, we demonstrate conductive and conformal MXene multilayer coatings that can undergo large-scale mechanical deformation while maintaining a conductivity as high as 2,000 S/m. MXene multilayers are successfully deposited onto flexible polymer sheet, stretchable poly(dimethylsiloxane), nylon fiber, cotton fabric, and glass. The coating shows a recoverable resistance response to bending (up to 2.5 mm bending radius) and stretching (up to 40% tensile strain). We demonstrated that the MXene multilayers could be used as strain sensors to topographically sense objects or materials deformation. We further demonstrated the water sorption and resistance response mechanism for the MXene multilayers for humidity sensing. The MXene multilayers exhibited fast response and recovery times upon humidity change, which exceeded those of most humidity sensors and allowed a rapid response to dynamic changes in humidity (i.e., human respiration). Quartz crystal microbalance and ellipsometry supported the mechanism that, upon changing humidity, water molecules intercalate into the MXene/polyelectrolyte multilayer, resulting in an increase in the thickness and sheet-to-sheet distance, which then changes the tunneling resistance between MXene sheets. We anticipate that this discovery will allow for the implementation of MXene-based coatings onto the rapidly growing fields of noncontact medical diagnosis, noninvasive epidermal sensing, and environmental monitoring.