Web Release Date: March 5,
Liquid-Vapor Interface of Methanol-Water Mixtures: A Molecular Dynamics Study
Department of Chemistry, University of Wisconsin, Parkside, 900 Wood Road, Box 2000, Kenosha, Wisconsin 53141-2000
Chemical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352
Received: September 24, 2004
In Final Form: November 11, 2004
Abstract:
Molecular dynamics simulations were carried out to investigate the structural and thermodynamic properties and variations in the dipole moments of the liquid-vapor interfaces of methanol-water mixtures. Various methanol-water compositions were simulated at room temperature. We found that methanol tends to concentrate at the interface, and the computed surface tension shows a composition dependence that is consistent with experimental measurements. The methanol molecule shows preferred orientation near the interface with the methyl group pointing into the vapor phase. The methanol in the mixture is found to have larger dipole moments than that of pure liquid methanol. The strong local field induced by the surrounding water molecules is partly the reason for this difference. The dependence of hydrogen-bonding patterns between methanol and water on the interface and the composition of the mixture is also discussed in the paper.
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