(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 MoS_2, as well as its applications in applications including membranes, microfluidic devices, and sensors.