Influence of hydrogen bonds and temperature on dielectric properties

Abstract

Dielectric properties have been evaluated by means of Molecular Dynamics simulations on two model systems made up by dipolar molecules. One of them mimics methanol, whereas the other differs from the former only in the ability of forming hydrogen bonds. Static dielectric properties such as permittivity and the Kirkwood factor have been evaluated, and results have been analyzed by considering the distribution of relative orientations between molecular dipoles. Dipole moment time correlation functions have also been evaluated. The relevance of contributions associated to autocorrelations of molecular dipoles and to cross-correlations between dipoles belonging to different molecules has been investigated. For methanol, the Debye approximation for the overall dipole moment correlation function is not valid at room temperature. The model applies when hydrogen bonds are suppressed, but it fails upon cooling the non-associated liquid. Important differences between relaxation times associated with dipole auto and cross-correlations as well as their relative relevance are at the root of the Debye model breakdown. *

A structure–dynamics relationship enables prediction of the water hydrogen bond exchange activation energy from experimental data

“…† We have plotted E a,X as a function of −TDDS ‡ for each water model in Fig. 4D-F and tted these data to eqn (13). While the observed correlations are strong (R 2 between 0.842 and 0.887), they are weaker than that found for the enthalpic correlations.…”

“…The ability of this network to quickly exchange these H-bonds is responsible for many of the noteworthy features of the neat liquid. [1][2][3][4] Under ambient conditions, H-bond exchanges play a critical role in most dynamical processes including diffusion, 5 reorientation, 6,7 viscosity, [8][9][10][11] dielectric relaxation, 12,13 structural rearrangements, 14,15 and chemical reactions. [16][17][18] Given that these exchanges play such a ubiquitous role, it is not surprising that they have received signicant attention.…”

Orientational dynamics in methanol: Influence of temperature and hydrogen bonding

“…The Debye rotational diffusion model [8] describes reasonably well the dynamics of non-associated liquids by considering that their molecules perform rotational Brownian motions [9]. It has been previously shown that methanol is a non-Debye fluid at room temperature [10], but its deviations from the Debye model for reorientation characteristic times are smaller than those obtained for water [11]. The extended jump model has proven to be successful in the analysis of molecular reorientation in hydrogen bonded liquids.…”