STRUCTURE OF CLUSTERS IN ETHANOL-WATER BINARY-SOLUTIONS STUDIED BY MASS-SPECTROMETRY AND X-RAY-DIFFRACTION

The structure of clusters in ethanol-water binary solutions at x(E) (ethanol mole fraction) greater than or equal to 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 (N-a) of the ethanol m-mer hydrates (5 < m < 15) in the mixtures at 0.2 less than or equal to x(E) less than or equal to 0.8 was found to be expressed by a function of the water mole fraction (x(w)), N-a = {(m/4.2)-1}(2) (x(w)+0.85), suggesting that the fundamental structure of ethanol polymer-hydrates is invariable in this region. An inflection point of N-a was found at x(E) approximate to 0.2. The radial distribution functions (RDFs) from X-ray measurements demonstrated a decrease of linear hydrogen bonds at 2.8 Angstrom with increasing x(E), while keeping the strongest peak at 4.8 Angstrom for 0.4 less than or equal to x(E) less than or equal to 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 less than or equal to x(E) less than or equal to 0.8.