Dielectric Constant of Water Confined in a Nanocavity

Abstract

The dielectric constant of water confined in a nanodimensional spherical cavity is calculated by means of molecular dynamics simulations. The simulations are carried out by using two different water models: soft sticky dipole and simple point charge/extended. Three different sizes of the confining cavity are considered for each water model. For both the models, the dielectric constant of water in the cavity is found to be significantly smaller than that of bulk water. A nearly 50% decrease of the dielectric constant is observed when water is confined in a cavity of about 12 Å in diameter. In the present models, there is no electrostatic interaction between water and the cavity surface, and thus, the reduction of the dielectric constant observed in this study is purely a result of confinement.

Transport in Proton Conductors for Fuel‐Cell Applications: Simulations, Elementary Reactions, and Phenomenology

“…Both experimental [119][120][121][122] and MD simulations [123][124][125][126] have revealed that water confined in systems such as reverse micelles and biological pores possesses a decreased polarity and rate of relaxation, and an increased degree of spatial and orientational order, when compared to bulk water. As such, assumptions of a constant dielectric constant for the water in the pore of a PEM (either that of bulk water or some other values) is clearly incorrect.…”

Dynamic polarizability, Cauchy moments, and the optical absorption spectrum of liquid water: A sequential molecular dynamics/quantum mechanical approach

“…In particular the absorption spectrum of water in the high-energy side and the role of HB on line broadening deserve more attention. Moreover, reliable theoretical approaches for the prediction of water electronic properties are useful for investigating the absorption spectra and dielectric properties of confined 25,26 and supercritical water, 27 which are much less understood.…”

Structure and dynamics of water in nanoscopic spheres and tubes

“…The fact that the water nanospheres with hydrophobic surfaces studied by Senapati and Chandra 61 also show a strong reduction in g K suggests that the main conditions for reducing the Kirkwood factor are the small size and centrosymmetric shape of the water nanodroplet. Interestingly, the simulations of Senapati and Chandra show that for hydrophobic surfaces the reduction in g K already disappears at comparatively small droplet sizes ( = 71 for r 0 = 1.2 nm), 61 whereas we find a reduction in g K that persists up to larger droplet sizes (see Fig. 4(b)).…”

“…Simulations by Senapati and Chandra have shown a 50% reduction of H 2 O for very small (0.61 nm radius) spherical water volumes that have no electrostatic interaction with the confining walls. 61 We believe that this reduction of the Kirkwood factor is due to an anti-parallel orientation of water molecules at opposing surfaces of the nanodroplet. In reverse micelles, the OH bond and dipoles of the water molecules at the surface point radially outward in order to hydrate the oxygen atoms of the Igepal surfactant.…”