THERMODYNAMIC AND STRUCTURAL-PROPERTIES OF METHANOL-WATER MIXTURES - EXPERIMENT, THEORY, AND MOLECULAR SIMULATION

We report a combined experimental, theoretical and molecular simulation study of the thermodynamics and structure of water-methanol mixtures. FTIR spectroscopic measurements in both the fundamental and overtone regions of the O-H stretch have been made over a wide range of concentration and temperature to obtain information on the energy of hydrogen-bonding and the concentrations of monomeric OH species. Theoretical work has been based on an extension of the cluster expansion theory of Wertheim. The FTIR measurements aid in determining the necessary intermolecular force parameters. The theory is used to predict the thermodynamic properties of both pure and mixed fluids, with particular emphasis on the excess properties of the mixture. Comparisons with experiment show moderately good agreement for this complex mixture. We also report Monte Carlo simulations for this mixture, using OPLS potentials for methanol-methanol and methanol-water interactions and several different potentials for the water-water interaction. We find that the resulting excess properties are sensitive to the water-water potential chosen. The CC potential for water gives quite good agreement with the experimental data.