A NEUTRON-DIFFRACTION STUDY OF DIMETHYL-SULFOXIDE WATER MIXTURES

Neutron diffraction with hydrogen/deuterium isotope substitution is used to investigate the structure of water in concentrated dimethyl sulphoxide (DMSO) aqueous solutions. Partial structure factors and pair correlation functions involving the hydrogen atom on the water molecule are determined. Water structure is not found to be strongly affected by the presence of DMSO. However, the percentage of water molecules which hydrogen bond to themselves is substantially reduced compared to pure water, with a large proportion of the hydrogens available for bonding associated with the lone pairs on the DMSO. These experimental findings are in good agreement with the assumptions made in the simple mean-field type model for hydrogen-bonded mixtures, developed by Luzar [J. Chem. Phys. 91, 3603 (1989)]. A general scheme for analyzing experimental data on the HH and OH pair correlation functions in terms of coordination numbers is presented. The hydrogen-hydrogen correlation in the solvent (water) is also used to discuss the interparticle correlations between solute (DMSO) particles.