STRUCTURE OF WATER-METHANOL BINARY-MIXTURES - ROLE OF THE WATER WATER INTERACTION

The structure of water-methanol mixtures at 298.15 K and 1 bar is investigated by means of the extended RISM equation with an HNC-like closure. Radial distribution functions between interaction sites are obtained for the mixture at room temperature and pressure. The OPLS model is used for the methanol-methanol interaction; both the MCY and TIPS potentials are used for the water-water interaction. An association of hydrophobic groups in methanol can be observed in water-rich mixtures. The association of hydrophobic groups is of the solvent-separated type for the MCY water potential, while the direct contact of hydrophobic groups is favourable for the TIPS water. The qualitative, difference in the character of association is examined in terms of the differences in the water-water interaction. It is found that the difference in the characteristics of the association arises mainly from the short-range repulsion between oxygen atoms rather than the difference in the Coulombic interaction.