(637d) Development of All-Atomistic Polarizable Force Fields for Molecular Simulations of Electronic Polarization Effects in Interfacial Phenomena

Molecular simulations along with the tools of statistical mechanics can provide vital mechanistic insights on the behavior of pure fluids and electrolytes at solid/water interfaces, which has broad applications in several scientific disciplines, including electrochemistry, membrane science, colloids, biophysics, and catalysis. At any solid/water interface, because water is a polar solvent and salt ions are charged species, they can exert strong electric fields which can in turn result in a significant electronic polarization of the solid. However, previous molecular dynamics (MD) simulation studies have typically neglected electronic polarization effects due to challenges associated with self-consistently modeling the ion–solid and water–solid polarization interactions at the solid/water interface. Here, we present a theoretical framework to self-consistently model electronic polarization effects at solid/water interfaces, and then apply it to investigate the graphene/water interface, which has shown tremendous promise for energy- and membrane-based applications. Using quantum chemical simulations carried out using the symmetry-adapted perturbation theory (SAPT), we first developed all-atomistic polarizable force fields which can accurately model the interactions of water molecules and salt ions with graphitic surfaces. Next, we applied our theoretical framework to carry out a comprehensive investigation of the role of electronic polarization effects on the contact angle of pure water on graphite (multilayer graphene). We demonstrate that the graphene-water polarization interactions have a significant impact on the interfacial entropy of water compared to the graphene–water dispersion interactions. This results in a significant energy–entropy compensation in the calculated solid–liquid (graphite –water) work of adhesion, which directly determines the water contact angle on graphite. We show that the simulated contact angle of water on graphite obtained using our all-atomistic polarizable force field is in quantitative agreement with the available experimental data, whereas an implicit modeling of the graphene–water polarization energy using a Lennard–Jones (LJ) potential results in a significant underestimation of the water contact angle by as much as 23°. Finally, in addition to modeling pure water, we also model electrolytes containing salt ions at the graphene/water interface. In this case, our study shows how electronic polarization effects contribute to a coupling between the graphene–ion and graphene–water interactions via electric fields, which is completely disregarded when the intermolecular interactions are instead modeled using pair-wise additive potentials, such as the LJ potential. In summary, we present a multiscale methodology to model electronic polarization effects using a combination of quantum chemical and classical MD simulations, and highlight the role of polarization interactions on the chemical physics of wetting and salt ion adsorption at the graphene/water interface.