Dynamics of 2D Monolayer Confined Water in Hydrophobic and Charged Environments

TL;DR

This study uses molecular dynamics to explore how water behaves in nanoconfined environments, revealing that surface polarity and confinement strongly influence water dynamics, vibrational modes, and coupling scales.

Contribution

It provides new insights into the effects of hydrophilic and hydrophobic confinement on water dynamics, including anomalous superdiffusive behavior and vibrational density of states modifications.

Findings

Arrhenius dynamics with high activation energy in extreme confinement

Superdiffusive intermediate time scale in polar confinement

Enhanced low-frequency collective modes in confined water

Abstract

Using molecular dynamics simulations we study the dynamics of a water-like TIP5P model of water in hydrophilic and hydrophobic confinement. We find that in case of extreme nanocofinement such that there is only one molecular layer of water between the confinement surface, the dynamics of water remains Arrhenius with a very high activation energy up to high temperatures. In case of polar (hydrophilic) confinement, The intermediate time scale dynamics of water is drastically modified presumably due to the transient coupling of dipoles with the effective electric field due to the surface charges. Specifically, we find that in the presence of the polar surfaces, the dynamics of monolayer water shows anomalous region -- namely the lateral mean square displacement displays a distinct superdiffusive intermediate time scale behavior in addition to ballistic and diffusive regimes. We explain these finding by proposing a simple model. Furthermore, we find that confinement and the surface polarity changes the vibrational density of states specifically we see the enhancement of the low frequency collective modes in confinement compared to bulk water. Finally, we find that the length scale of translational-orientational coupling increases with the strength of the polarity of the surface.