Ti₃C₂T_x MXene Liquid Crystal: Access to Create Background-Free and Easy-Made Alignment Medium

The formation of lyotropic liquid crystals (LCs) in two-dimensional (2D) colloidal dispersions enables the production of mesoscopic/macroscopic ordered materials from nanoscale building blocks. In contrast to graphene oxide (GO) LCs, the practical applications of MXene LCs are less exploited. This study bridges the gap by utilizing a simple and versatile fabrication method to prepare Ti3C2Tx MXene LC that can be applied as a background-free alignment medium for the residual dipolar coupling (RDC) measurement of organic molecules. Ti3C2Tx LC displays the size- and concentration-dependent alignment degree. Ti3C2Tx nanoflakes with an average size of around 600 nm can provide the quadrupolar 2H splitting of 71 Hz at a concentration of 50 mg/mL and show excellent fluidity at such a high concentration. Compared with other alignment media, Ti3C2Tx LC exhibits the features of no-background and narrow line broadening, which actualizes the acquirement of clean and high-quality NMR spectra for the accurate RDC extraction. Notably, the alignment of LCs is determined to be maintainable in the redispersed solution after freeze-drying, providing the great convenience for the preparation of alignment Ti3C2Tx media, long-term sample preservation, and quantitative evaluation of alignment degree. Meanwhile, the alignment LC media for RDC measurement can be established in other MXenes such as Ti2CTx and Ti3CNTx. Collectively, our findings demonstrate the potential of creating various alignment media from the fascinating MXene family.