Properties of hydrogen bonded network in ethanol-water liquid mixtures as a function of temperature: diffraction experiments and computer simulations

TL;DR

This study combines diffraction experiments and molecular dynamics simulations to analyze how hydrogen bonded networks in ethanol-water mixtures evolve with temperature and composition, revealing percolation phenomena and structural details.

Contribution

It provides comprehensive experimental and computational insights into hydrogen bonding and network percolation in ethanol-water mixtures across various temperatures and compositions.

Findings

Hydrogen bonded cycles are dominant up to 70% ethanol at room temperature.

Percolation occurs in the mixture at low temperatures even with 90% ethanol.

Water sub-network percolates at around 50% ethanol at room temperature.

Abstract

New X-ray and neutron diffraction experiments have been performed on ethanol-water mixtures as a function of decreasing temperature, so that such diffraction data are now available over the entire composition range. Extensive molecular dynamics simulations show that the all-atom interatomic potentials applied are adequate for gaining insight of the hydrogen bonded network structure, as well as of its changes on cooling. Various tools have been exploited for revealing details concerning hydrogen bonding, like determining H-bond acceptor and donor sites, calculating cluster size distributions and cluster topologies, as well as computing the Laplace spectra and fractal dimensions of the networks. It is found that 5-membered hydrogen bonded cycles are dominant up to an ethanol content of 70% at room temperature, above which concentration ring structures nearly disappear. Percolation has been given special attention, so that it could be shown that at low temperature, close to the freezing point even the mixture with 90% ethanol possesses a 3D percolating network. Moreover, the water sub-network also percolates even at room temperature, with a percolation transition occurring around 50% ethanol.