Layer-by-Layer Assembly of Two-Dimensional MXene Nanosheets with Polyelectrolyte and Emerging Applications

A broad family of two-dimensional ceramic nanosheets referred to as MXenes have caught the world’s attention because of their wide compositional diversity and tailorability to different engineering applications, including energy storage, catalysis, electromagnetic interference shielding, sensors, composites, and batteries. One challenge is to translate these applications into a thin-film platform. This presentation will discuss the water-based solution-assembly of two-dimensional MXene nanosheets with polyelectrolyte using the layer-by-layer (LbL) assembly technique. This approach produces conformal MXene-based coatings on a variety of surfaces including hydrophobic poly(dimethylsiloxane), glass, thread and fiber, and silicon. The result is a conformal coating consisting of a brick-and-mortar-type architecture with tunable layer thicknesses. We take advantage of the MXene-polymer morphology to demonstrate strain, humidity, and pH sensors, as well as electrodes for electrochemical energy storage. In our latest work, we examine the formation of heterostructures, in which MXenes are precisely placed with nanometer precision in thin films, separated by polymeric regions. We report the emergence of structural color in these Ti₃C₂T_z MXene-polyelectrolyte LbL heterostructures with controlled block thicknesses. The block thickness and spatial placement of MXene is controlled by the assembly’s salt concentration and number of layer pairs. This work demonstrates that optical characteristics of MXene/polyelectrolyte heterostructures depend on MXene content and placement, while deepening the understanding of MXenes within structural color films. Last, we close with a discussion of the gas-barrier properties of MXene LbL assemblies.