Quantitative Modeling of MoS₂–Solvent Interfaces: Predicting Contact Angles and Exfoliation Performance using Molecular Dynamics

Abstract

The large-scale synthesis of molybdenum disulfide (MoS 2 ) using liquid-phase exfoliation, as well as several of its intended applications, including desalination membranes and biosensors, involve liquids coming into intimate contact with MoS 2 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 MoS 2 currently available in the literature incorrectly describe not only the cohesive interactions between layers of MoS 2 but also the adhesive interactions of MoS 2 with liquids such as water. Here, we develop a set of force-field parameters that reproduce the properties of bulk 2H-MoS 2 , 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 MoS 2 −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 MoS 2 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 MoS 2 flakes, including the colloidal stability of the resulting dispersion. Our new force field enables an accurate description of MoS 2 interfaces and will hopefully pave the way for simulation-aided design in applications including membranes, microfluidic devices, and sensors.

Mechanosensitive Ion Permeation across Subnanoporous MoS2 Monolayers

“…Thus, given the considerable degree of ionicity of bonds in bulk MoS 2 monolayers, 9 a straightforward estimate of the total charge of the pore and the surrounding lattice is the opposite of the sum of the bulk partial atomic charges removed to create a given pore structure. Given the bulk partial charges of q Mo = +0.5e and q S = -0.25e, 9 the structures in Fig. 1e and Fig.…”

Exfoliation of graphene and fluorographene in molecular and ionic liquids

“…This is the argument that "like dissolves like": the solute-solvent interacton energy should be commensurate with the cohesive energy of the solvent, otherwise one of them will have too strong a tendency to aggregate not favouring the formation of a dispersion. However, this is not the sole descriptor defining a good solvent: the planarity of the amides contributes to an easier intercalation between layers of the 2D material during the exfoliation process [16,17].…”

“…This descriptor related to molecular shape is not captured easily by quantities such as surface tension or solubility parameters. Next we investigated MoS 2 [17] and learned that the polarity of Mo S bonds has a negligible effect on the contact angle of water [18]. These examples show that subtle and sometimes unexpected factors play important roles.…”

Ion transport across solid-state ion channels perturbed by directed strain

“…We performed an angular sweep of uniaxial strain (ε = 0.04) applied to a monolayer MoS2 membrane featuring nine such pores. The simulation setup with 0.5M of aqueous NaCl was similar to that described above for grapheneembedded N4O2 pores and used a refined parameter set [32] utilized in our earlier work [11].…”