Stable colloidal dispersion of octylated Ti3C2-MXenes in a nonpolar solvent

Two-dimensional (2D) early transition metal carbides and/or nitrides (MXenes) have shown significant potential in a wide variety of applications. The majority of MXene research has utilized aqueous colloidal dispersions of MXenes because of the unique hydrophilicity of the MXene surface. In some cases, however, aqueous dispersions have various disadvantages such as the degradation of MXenes in long-term storage, incompatibility with water-insoluble polymers, and dewetting on low-surface-energy substrates. Herein, we demonstrated a stable nonpolar colloidal dispersion of MXenes chemically grafted with lipophilic octyltriethoxysilanes (MX@OTS). A high grafting density of OTS on the MXene surface was achieved by employing a strong acid polyelectrolyte, poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), as an OTS (water insoluble)-in-water emulsifier while the reaction was carried out in the aqueous media in which the hydrophilic MXenes showed the best dispersion. The remarkable hydrophobicity of these octylated MXenes was demonstrated by a high water-contact angle on the macroscopic MX@OTS surface as well as the high interfacial tension between the MX@OTS-in-hexane dispersion and water, which was almost identical to that for pure hexane/water. Despite the negligible surface charging, the hydrophobic MX@OTS showed excellent colloidal stability in very nonpolar hexanes over four weeks.