Properties of Hydrogen-Bonded Networks in Ethanol–Water Liquid Mixtures as a Function of Temperature: Diffraction Experiments and Computer Simulations

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 x eth = 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 ( x eth = 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 x eth = 0.5.

Temperature-dependent structure of 1-propanol/water mixtures: X-ray diffraction experiments and computer simulations at low and high alcohol contents

“…Percolating of the H-bonded network was reported up to higher alcohol concentrations as the temperature decreases in 2-propanol-water [27] and ethanol-water [28] mixtures. However, on the temperature dependence of the structure of 1-propanolwater mixtures, according to our best of knowledge, only a small angle neutron scattering experiment can be found in the literature [9].…”

“…The evolution of the structure of alcohol-water mixtures with decreasing temperature has been examined in methanol-water, ethanol-water and 2-propanol-water mixtures [20][21][22][23][24][25][26][27][28].…”

Non-monotonic composition dependence of the breakdown of Stokes–Einstein relation for water in aqueous solutions of ethanol and 1-propanol: explanation using translational jump-diffusion approach

“…Many of these studies have indicated anomalous properties of this mixture. Strong non-idealities are observed in thermodynamic, structural, 1–21 and transport properties, 10,12,13,16,22–40 like diffusion and viscosity. Most of these properties show nonmonotonic composition dependence with the extremum at ∼0.20 mole fraction of ethanol.…”

Dynamical Anomaly of Aqueous Amphiphilic Solutions: Connection to Solution H-Bond Fluctuation Dynamics?

“…Several simulation and computational studies have examined the hydrophobic hydration-induced modification in solution structure and the role of interspecies H-bonding in binary aqueous mixtures of TBA 14 − 23 and other alcohols. 24 − 29 Interestingly, studies employing TBA as an amphiphile are relatively more in number, although investigations employing other amphiphiles also focused on solute-induced distortion of water structure, solution heterogeneity, and solution dynamics. 30 − 32 The reason for employing TBA emerges from the fact that TBA possesses the largest aliphatic group among monohydroxy alcohols that are miscible with water at any proportion.…”