Synthesis and characterization of solvent-free ionic molybdenum disulphide (MoS2) nanofluids

Abstract

A development of the novel and stable solvent-free ionic MoS2 nanofluids by a facile and scalable hydrothermal method is presented. The nanofluids were synthesized by surface functionalizing nanoscale MoS2 from hydrothermal synthesis with a charged corona, and ionically tethering with oligomeric chains as a canopy. The structures and properties of the nanofluids were characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR, 1H), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA) and ARES rheometer. The obtained solvent-free nanofluids are homogeneous, stable amber-like fluids with no evidence of phase separation. The nanofluids could be easily dispersed in both aqueous and organic solvents to form transparent and stable liquids due to the ionic nature and the presence of oligomeric polymer chains. It was found that the solvent-free nanofluids with up to 32 wt% inorganic content show Newtonian rheological behaviors due to the high graft density and uniform dispersion of inorganic cores, indicating that the nanofluids would have a stable lubricating performance. As reported in our previous communication, the nanofluids showing lower, more stable friction coefficients of less than 0.1 with self-healing lubricating behaviors. For deeper understanding of the nanofluids, the details of synthesis, chemical structures, rheological behaviors and molecular dynamics of the nanofluids were investigated in details. The rheological behaviors can be tailored by varying the grafting density of the canopy. Dynamic results of the canopy of the MoS2 nanofluids show that inorganic MoS2 cores have hindrance effect on the canopy segmental motions above 253 K due to their effect to the mobility of anions and the departing-recombining motions between the paired cations and anions.