Coatings and thin films are found in everyday objects as a means to introduce functionality or enhance the performance of the underlying substrate. We examine layer-by-layer (LbL) assembly as a versatile means to produce conformal coatings with functionalities ranging from conductive coatings to sensors using the assembly of oppositely charged polyelectrolytes and 2D MXene nanosheets. MXenes are a class of two-dimensional transition metal carbides possessing hydrophilicity and metal-like conductivity. They are emerging as an interesting alternative to graphene sheets, yet they are notoriously difficult to process. Specifically, we assemble negatively charged Ti3C2Tx MXene sheets with positively charged poly(diallyldimethylammonium chloride) using simple immersion-based LbL assembly or spray-on LbL assembly, suitable for deposition over large areas. We demonstrate the assembly on a variety of surfaces including PET, glass, nylon thread, cotton fabric, and PDMS. Our processing approach yields flexible, stretchable conductive MXene-polyelectrolyte nanocomposite coatings. These act as reversible strain sensors, facilitated by the self-healing of the MXene-polyelectrolyte electrostatic bonds. We also present the dynamic response of these multilayers to humidity and human respiration. The MXene/polyelectrolyte multilayer films exhibit response and recovery times exceeding those of most humidity sensors. 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. Broadly speaking, the MXene-polyelectrolyte morphology allows one to tune physical properties by adjusting the interlayer spacing between the 2D nanosheets and the responsiveness of the polyelectrolyte to external stimuli.

Advanced functional layer-by-layer assemblies containing MXenes and polyelectrolytes

2019 Fall National Meeting

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