(490c) Development of a New Molecular Dynamics Force Field to Model Intermolecular Interactions at MoS2 Interfaces: Application to Liquid-Phase Exfoliation
The controlled synthesis of molybdenum disulfide (MoS2) using liquid-phase exfoliation, as well as several of its proposed applications, involve liquids coming into intimate contact with MoS2 surfaces. Molecular dynamics (MD) simulations offer a robust methodology to investigate nanomaterial/liquid interactions involving weak van der Waals forces. However, MD force fields for MoS2 currently available in the literature incorrectly describe not only the cohesive interactions between layers of MoS2, but also the adhesive interactions of MoS2 with liquids such as water. Here, we develop a set of force-field parameters that reproduce the properties of bulk 2-H molybdenite, with special attention to the distinction between the covalent, intra-layer terms and the non-covalent, inter-layer Coulombic and van der Waals interactions. The resulting model is compatible with MD force fields for organic compounds, and can correctly describe the interactions of MoS2 with liquids, yielding excellent agreement with experimental contact angles for water and diiodomethane. Potential of mean force (PMF) calculations using various solvents, including isopropanol (IPA), water (H2O), dimethyl sulfoxide (DMSO), dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP), demonstrate that the use of our force field can explain the current selection of solvents used in experimental studies of the liquid-phase exfoliation of MoS2 flakes, as well as the observed colloidal stability of the resulting dispersion. Our new force field enables an accurate description of MoS2 interfaces, and will pave the way for the simulation-aided design of solvent media for the exfoliation of MoS2, as well as its applications in applications including membranes, microfluidic devices, and sensors.