Molecular dynamics simulation of behaviour of water in nano-confined ionic liquid--water mixtures

TL;DR

This study uses molecular dynamics simulations to explore how water behaves when confined at the nanoscale between graphene sheets in ionic liquid-water mixtures, revealing adsorption patterns and structural changes.

Contribution

It provides new insights into water behavior under nanoconfinement in ionic liquids, including adsorption phenomena and structural transitions, modeled with a two-level statistical approach.

Findings

Water adsorbs on positively charged graphene surfaces.

Water is depleted near neutral and negatively charged surfaces.

Structural and dynamical changes occur in confined water layers.

Abstract

This work describes the behaviour of water molecules in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid under nanoconfinement between graphene sheets. By means of molecular dynamics simulations, an adsorption of water molecules at the graphene surface is studied. A depletion of water molecules in the vicinity of the neutral and negatively charged graphene surfaces and their adsorption at the positively charged surface are observed in line with the preferential hydration of the ionic liquid anions. The findings are appropriately described using a two-level statistical model. The confinement effect on the structure and dynamics of the mixtures is thoroughly analyzed using the density and the potential of mean force profiles, as well as by the vibrational densities of states of water molecules near the graphene surface. The orientation of water molecules and the water-induced structural transitions in the layer closest to the graphene surface are also discussed.