Nanoconfined Water Phase Transitions in Infinite Graphene Slits: Molecular Dynamics Simulations and Mean-Field Insights

TL;DR

This study uses molecular dynamics and mean-field models to explore how nanoconfinement in infinite graphene slits induces unique water phase transitions at low pressures, highlighting the role of hydrogen bonding and phase hysteresis.

Contribution

It provides new insights into water behavior under nanoconfinement, demonstrating genuine phase transitions and the influence of graphene surfaces on hydrogen bond networks.

Findings

Hysteresis observed across all temperatures in infinite slits

Genuine phase transition identified at the nanoscale

Low pressure water uptake explained by mean-field lattice model

Abstract

Recent experimental and computational studies have demonstrated that nanoconfinement profoundly alters the phase behavior of water, facilitating complex phase transitions at pressures and temperatures far lower than typically observed in bulk systems. When combined with adsorption, nanoconfinement substantially enhances water uptake, primarily due to condensation occurring at the onset of the isotherm curve-a phenomenon intimately related to the facilitated formation of hydrogen bond networks. In this study, we adopt a dual approach to investigate water confined within infinite graphene slits. Our Molecular Dynamics simulations reveal hysteresis across all investigated temperatures. Unlike in finite slits, where hysteresis arises due to surface tension effects at the edges, in the case of infinite slits, the hysteresis is the result of a genuine phase transition at the nanoscale. We analyze the spatial and orientational arrangements of the water molecules, demonstrating how the graphene surface promotes the formation of a hydrogen bond network in the adjacent water layers. The remarkably low pressure required for water uptake in this nano-environment is explained at the mean-field level using a simple interacting lattice model. This is attributed to the exponential dependence of the critical pressure on the adsorbate-adsorbent interaction.