Molecular dynamics simulations of water confined in graphene nanochannels: From ambient to supercritical environments

We report results of molecular dynamics simulations of water at ambient, high-temperature and supercritical conditions inside a graphene slab 3.1 nm wide. The potential models we employed include a flexible SPC water force field, especially adjusted to reproduce the main features of the infrared spectrum of water at room temperature, and Lennard-Jones like forces between oxygen and carbon atoms. A thorough analysis of the structure, hydrogen bonding, dielectric, diffusion and spectroscopical properties of the system is presented. The main aim of the present work has been to compare all collected properties within a wide range of temperatures and densities and to explore the influence of thermodynamic and hydrophobic confinement effects on the microscopic structure and dynamics of the system. In route from ambient to supercritical environments, we observed structural weakening due to massive hydrogen-bond breaking, reduction of permittivity and residence times in selected regions, a gradual rise of water self-diffusion coefficients and the presence of spectral shifts related to changes in molecular and atomic vibrations.