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 into the hydrogen-bonded network structure, as well as into its changes on cooling. Various tools have been exploited for revealing details concerning hydrogen bonding, as a function of decreasing temperature and ethanol concentration, like determining the H-bond acceptor and donor sites, calculating the cluster-size distributions and cluster topologies, and 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 mole fraction xeth = 0.7 at room temperature, above which the concentrated ring structures nearly disappear. Percolation has been given special attention, so that it could be shown that at low temperatures, close to the freezing point, even the mixture with 90% ethanol (xeth = 0.9) possesses a three-dimensional (3D) percolating network. Moreover, the water subnetwork also percolates even at room temperature, with a percolation transition occurring around xeth = 0.5.
Highlights
The physicochemical properties of water−ethanol solutions have been among the most extensively studied subjects in the field of molecular liquids over the past few decades,[1−17] due to their high biological and chemical significance
X-ray and neutron diffraction measurements have been conducted on ethanol−water mixtures, as a function of temperature, down to the freezing points of the liquids
Article result of the new experiments, temperature-dependent X-ray structure factors are available for the entire composition range
Summary
The physicochemical properties of water−ethanol solutions have been among the most extensively studied subjects in the field of molecular liquids over the past few decades,[1−17] due to their high biological and chemical significance. Even though they are composed of two simple molecules, the behavior of their hydrogen-bonded network structures can be very complex, due to the competition between hydrophobic and hydrophilic interactions.[18−25] The characteristics of these networks can be greatly influenced by the concentration. We found that the number of hydrogen-bonded rings increased upon lowering the temperature, and that fivefold rings were in majority, especially at xeth > 0.1 ethanol concentrations
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