Modeling Simple Alcohols in Two Dimensions

Barbara Hribar-Lee1*, and Ken A. Dill2

1Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia.
E-mail: barbara.
2Department of Pharmaceutical Chemistry, University of California, San Francisco, California 94143-2240.

The alcohol-water mixtures were studied within a two-dimensional model. The MB model was used for modeling water and alcohol molecules were modeled as non-flexible chains consisting of two-dimensional Lennard-Jones disks with the first disk having two hydrogen-bonding arms. The model was explored using NPT Monte Carlo computer simulation. The results were compared with the experimental thermodynamic properties of methanol/water mixtures. The qualitative agreement was obtained for the excess volume of mixing, but due to the surface/volume effects not properly captured by two dimensional models, the excess enthalpy of mixing cannot be represented correctly by this model. Further, we studied the transfer of a single alcohol molecule into water, focusing on the trends exhibited by the methanol, ethanol, propanol, n-butanol series. While small alcohol molecules show the correct trend the flexibility of the alcohol molecules should be taken into account to improve the agreement for higher alcohols.

Key words:
MB model, alcohol/water mixtures, thermodynamics, Monte Carlo