Insights into Hydration Dynamics and Cooperative Interactions in Glycerol-Water Mixtures by Terahertz Dielectric Spectroscopy

TL;DR

This study investigates the relaxation dynamics and hydration structures in glycerol-water mixtures across various concentrations using terahertz dielectric spectroscopy and molecular dynamics simulations, revealing critical concentration effects and multiple polarization processes.

Contribution

It provides new insights into the molecular-level hydration structures and relaxation processes in glycerol-water mixtures, combining experimental spectroscopy with simulations.

Findings

Identification of multiple polarization processes with distinct time constants.

Discovery of a critical glycerol concentration (~7.5 mol %) affecting hydration shells.

Confirmation of experimental results through molecular dynamics simulations.

Abstract

We report relaxation dynamics of glycerol-water mixtures as probed by megahertz-to-terahertz dielectric spectroscopy in a frequency range from 50 MHz to 0.5 THz at room temperature. The dielectric relaxation spectra reveal several polarization processes at the molecular level with different time constants and dielectric strengths, providing an understanding of the hydrogen-bonding network in glycerol-water mixtures. We have determined the structure of hydration shells around glycerol molecules and the dynamics of bound water as a function of glycerol concentration in solutions using the Debye relaxation model. The experimental results show the existence of a critical glycerol concentration of ~7.5 mol %, which is related to the number of water molecules in the hydration layer around a glycerol molecule. At higher glycerol concentrations, water molecules dispersed in a glycerol network become abundant and eventually dominate and four distinct relaxation processes emerge in the mixtures. The relaxation dynamics and hydration structure in glycerol-water mixtures are further probed with molecular dynamics simulations, which confirm the physical picture revealed by the dielectric spectroscopy.