Surfactant-Free Polar-to-Nonpolar Phase Transfer of Exfoliated MoS2 Two-Dimensional Colloids.

Exfoliation of lamellar materials into their corresponding layers represented a breakthrough, owing to the outstanding properties arising from the nanometric thickness confinement. Among the cleavage techniques, liquid-phase exfoliation is now on the rise because it is scalable and leads to easy-to-manipulate colloids. However, all appropriate exfoliating solvents exhibit strong polarity, which greatly restricts the scope of feasible functionalization or processing of the resulting flakes. Here, this scope is extended: nanosheets exfoliated in a polar medium are demonstrated to properly disperse in a nonpolar solvent. To that purpose, suspensions of molybdenum disulfide flakes were prepared in isopropanol/water and a phase transfer of the nanosheets to chloroform was developed by flocculation and redispersion/centrifugation sequences, without any assisting surfactant. The colloidal stability of the nanosheets in chloroform was found to be governed by their lateral dimensions and, although lower than in polar media, proved to be high enough to open the way to subsequent functionalization or processing of the flakes in nonpolar media.