Quantitative Modeling of MoS 2 –Solvent Interfaces: Predicting Contact Angles and Exfoliation Performance using Molecular Dynamics
Résumé
The large-scale synthesis of molybdenum disulfide (MoS2) using liquid-phase exfoliation, as well as several of its intended applications, including desalination membranes and biosensors, 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 2H-MoS2, with special attention to the distinction between the covalent, intralayer terms and the noncovalent, interlayer Coulombic and van der Waals interactions. The resulting force field is compatible with MD force fields for liquids and can correctly describe interactions at MoS2–liquid interfaces, yielding excellent agreement with experimental contact angles for water (a polar solvent) and diiodomethane (a nonpolar solvent). In light of these results, previously published simulations studies on the desalination potential and biocompatibility of MoS2 devices need to be reevaluated. Potential of mean force (PMF) calculations demonstrate that use of our new force field can explain the current selection of solvents used in experimental studies of the liquid-phase exfoliation of MoS2 flakes, including the colloidal stability of the resulting dispersion. Our new force field enables an accurate description of MoS2 interfaces and will hopefully pave the way for simulation-aided design in applications including membranes, microfluidic devices, and sensors.