Additive-Free MXene Liquid Crystals and Fibers

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 Ti₃C₂T _<i>x</i> 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 Ti₃C₂T _<i>x</i> flake size in the ink formulation, coagulation bath, and spinning parameters, we control the morphology of the MXene fibers. The wet-spun Ti₃C₂T _<i>x</i> fibers show a high electrical conductivity of ∼7750 S cm^-1, surpassing existing nanomaterial-based fibers. A high volumetric capacitance of ∼1265 F cm^-3 makes Ti₃C₂T _<i>x</i> fibers promising for fiber-shaped supercapacitor devices. We also show that Ti₃C₂T _<i>x</i> fibers can be used as heaters. Notably, the nematic LC phase can be achieved in other MXenes (Mo₂Ti₂C₃T _<i>x</i> and Ti₂CT _<i>x</i> ) and in various organic solvents, suggesting the widespread LC behavior of MXene inks.