Altered Dielectric Behaviour, Structure and Dynamics of Nanoconfined Dipolar Liquids: Signatures of Enhanced Cooperativity

TL;DR

This study investigates how nanoconfinement affects the dielectric properties, structure, and dynamics of dipolar liquids like water and Stockmayer fluids, revealing enhanced cooperativity and anomalous relaxation behaviors at nanoscale confinement.

Contribution

It provides new insights into the altered dielectric behavior and dynamics of dipolar liquids under nanoconfinement, highlighting the importance of surface interactions and size effects.

Findings

Water's Kirkwood correlation factor remains small under confinement.

Confined water exhibits bimodal 1/f noise in dipole correlation.

Dielectric constant shows strong size dependence and slow convergence.

Abstract

Spherical confinement can alter the properties of a dipolar fluid in several different ways. In an atomistic molecular dynamics simulation study of two different dipolar liquids (SPC/E water and a model Stockmayer fluid) confined to nanocavities of different radii ranging from Rc=1nm to 4nm, we find that the Kirkwood correlation factor remains surprisingly small in water, but not so in model Stockmayer liquid. This gives rise to an anomalous ultrafast relaxation of the total dipole moment time correlation function (DMTCF). The static dielectric constant of water under nanoconfinement (computed by employing Clausius-Mossotti equation, the only exact relation) exhibits a strong dependence on the size of the nanocavity with a remarkably slow convergence to the bulk value. Interestingly, the value of the volume becomes ambiguous in this nanoworld. It is determined by the liquid-surface interaction potential and is to be treated with care because of the sensitivity of the Clausius-Mossotti equation to the volume of the nanosphere. We discover that the DMTCF for confined water exhibit a bimodal 1/f noise power spectrum. We also comment on the applicability of certain theoretical formalisms that become dubious in the nanoworld.