How pressure affects confine water inside different nanoslits

Abstract

Nanoslits composed of different layered nanomaterials attract great attention in the theoretical and experimental investigations of nanofluidic devices due to their geometric simplicity and unique surface properties. Although many efforts have witnessed simulations of water molecules inside slit-like nanochannels formed by graphenes, the thermodynamic properties and transport behavior of water inside nanoslits formed by different two-dimensional materials are seldom investigated. In this paper, we choose nanoslits formed by graphene, boron nitride (hBN), and molybdenum disulfide (MoS₂) as models, and study the water properties inside these nanoslits using traditional molecular dynamics simulations at different pressures. It is shown that water molecules can form a planar square at high pressure (10 kbar) in all three types of nanoslit. The nanoslits affect diffusion coefficient, orientation of water molecules, number of hydrogen bonds and life-time of hydrogen bonding significantly. The self-diffusion coefficients of water molecules in different nanoslits are all lower than that of bulk water. The diffusion coefficients are significantly affected by the special ordered structure of water, which is caused by the unique surface structure of the nanoslit. The results of the present work will be helpful to understand the unique behavior of confined water in nanoslits composed of different nanomaterials and provide theoretical guidance for many applications, such as desalination and nano-energy conversion.