Measurement of Two Solvation Regimes in Water-Ethanol Mixtures Using X-Ray Compton Scattering

Abstract

Water-ethanol mixtures exhibit interesting anomalies in their macroscopic properties. Despite a lot of research, the origin of the anomalies and the microscopic structure itself is still far from completely known. We have utilized the synchrotron x-ray Compton scattering technique to elucidate the structure of aqueous ethanol from a new experimental perspective. The technique is uniquely sensitive to the local molecular geometries at the angstrom and subangstrom scales. The experiments reveal two distinct mixing regimes in terms of geometry: the dilute 5 mol % and the concentrated >15 mol % regimes. By comparing with pure liquids, the former regime is characterized by an intramolecular and the latter by an intermolecular change. The findings bring new light to evaluating the hypothesis of formation of clathratelike structures at the dilute concentrations.

ERKALE—A flexible program package for X‐ray properties of atoms and molecules

“…Difference profiles have been successfully used in studying, for example, temperature-dependent hydrogen bond networks in water, [99,100] configurational energetics in ice, [101] and solvation in water-ethanol mixtures. [102] Completeness-optimized basis sets…”

Hydrogen bonding in the ethanol–water dimer

“…They exhibit many thermodynamic anomalies, such as a negative entropy of mixing, for example, which are believed to originate from incomplete mixing on the microscopic scale. 5 Elucidating the structure and dynamics of hydrogen bonding of the ethanol-water clusters, especially the dimer, may inform such studies.…”

Structure and thermodynamics of core-softened models for alcohols

“…On the other hand, the presence of both the hydroxyl group and the organic radical, usually nonpolar, allows for the interaction with a huge number of organic and inorganic compounds, making alcohols good solvents. In recent years, many efforts have been devoted to experimentally investigate physical properties of small alcohols, encompassing their solvent properties, 1,2 mixtures with water, [3][4][5][6] and phase behavior in general. 7,8 At the same time, computer simulations and theoretical approaches have proved to constitute important tools in supporting experimental investigations: in particular, a significant number of numerical studies have focused on structure, [9][10][11][12] thermodynamics, and phase equilibria 13 of these alcohols.…”