Additive-Free MXene Liquid Crystals and Fibers

Copyright © 2020 American Chemical Society. The discovery of liquid crystalline (LC) phases in dispersions of two-dimensional (2D) materials has enabled the development of macroscopically aligned three-dimensional (3D) macrostructures. Here, we report the first experimental observation of self-assembled LC phases in aqueous Ti3C2Tx MXene inks without using LC additives, binders, or stabilizing agents. We show that the transition concentration from the isotropic to nematic phase is influenced by the aspect ratio of MXene flakes. The formation of the nematic LC phase makes it possible to produce fibers from MXenes using a wet-spinning method. By changing the Ti3C2Tx flake size in the ink formulation, coagulation bath, and spinning parameters, we control the morphology of the MXene fibers. The wet-spun Ti3C2Tx fibers show a high electrical conductivity of â7750 S cm-1, surpassing existing nanomaterial-based fibers. A high volumetric capacitance of 265 F cm-3 makes Ti3C2Tx fibers promising for fiber-shaped supercapacitor devices. We also show that Ti3C2Tx fibers can be used as heaters. Notably, the nematic LC phase can be achieved in other MXenes (Mo2Ti2C3Tx and Ti2CTx) and in various organic solvents, suggesting the widespread LC behavior of MXene inks.