Structure of Clusters in Ethanol–Water Binary Solutions Studied by Mass Spectrometry and X-Ray Diffraction

Abstract

The structure of clusters in ethanol–water binary solutions at xE (ethanol mole fraction) ≥ 0.2 was investigated by the mass-spectrometric analysis of clusters isolated from liquid droplets and X-ray diffraction measurements of the intact solution. The average number of water molecules (Na) of the ethanol m-mer hydrates (5 < m < 15) in the mixtures at 0.2 ≤ xE ≤ 0.8 was found to be expressed by a function of the water mole fraction (xw), Na = {(m/4.2) − 1}2 (xw + 0.85), suggesting that the fundamental structure of ethanol polymer-hydrates is invariable in this region. An inflection point of Na was found at xE ≈ 0.2. The radial distribution functions (RDFs) from X-ray measurements demonstrated a decrease of linear hydrogen bonds at 2.8 Å with increasing xE, while keeping the strongest peak at 4.8 Å for 0.4 ≤ xE ≤ 1.0. On the basis of a composition analysis of the mass spectra and the concentration dependence of RDFs, we propose the most likely model of ethanol–water binary clusters formed in the region 0.2 ≤ xE ≤ 0.8.

Effect of ultrasound on ester hydrolysis in aqueous ethanol

“…In this region, a large number of ethanol-water bonds are formed, and water-water bonds are broken. All of these results have led to a cluster model of a stacked ethanol core and a thin water shell [40,41]. The observations for diluted aqueous solutions of ethanol suggested the evolution of an ethanol polymer structure and a complete breakdown of the bulk water structure at X EtOH > 0.1.…”

“…Recent spectroscopic, X-ray diffraction, and mass spectrometric investigations have shed light on the structure of ethanol-water solutions [40][41][42]. It has been concluded that small additions of ethanol in the range of 0 < X EtOH < 0.08 (X EtOH is the ethanol molar ratio) exert a strong structuremaking effect accompanied by an increase in the self-association of water molecules.…”

Large-Angle X-ray Scattering Investigation of the Structure of 2-Propanol–Water Mixtures

“…The corrected intensities were normalized to electron units in a stoichiometric volume containing one oxygen atom of 2-propanol and / or water by conventional methods [20 -22]. A structure function, i(s), and a radial distribution function (RDF) for each sample were obtained as described [15]. These treatments of the LAXS data were carried out with program KURVLR [23].…”

“…When 2-propanol molecules are added to water, they will also be stabilized in the tetrahedral-like structure of water through hydrogen bonds between 2-propanol and water molecules, and an enthalpic gain due to the stabilization of 2-propanol molecules is largest at x 2pr 0.1. For methanol-water and ethanol-water mixtures, the minima of the heats of mixing are observed at x M 0.3 and x E 0.2, respectively, where the structural transition of dominant clusters from the tetrahedrallike structure of water to hydrogen-bonded alcohol chains takes place [13,15]. Thus, the minimum of the heat of mixing of 2-propanol-water mixtures is observed at the lowest alcohol content among the mixtures.…”

High Frequency Spectroscopic Study of the Bound State of Water in PEG-H2O System during Heating from Frozen State

“…Using HFS, researchers have studied the changes of clustering structure between water and organic molecules in water-alcohol systems, where the characteristic and discontinuous changes of resonance frequencies have been observed. 14 Various changes in solution structure have been reported in the measurements of X-ray diffraction, 15 mass analysis, 16,17 NMR, [18][19][20] Raman scattering, 21 and time-domain reflectmetry (TDR). 22 The results obtained by these measurements are basically in good agreement with those obtained by HFS study.…”