Structure of Mixtures of Water and Methanol Derived from Their Cohesive Energy Densities and Internal Pressures from Subambient Temperatures to 473 K.

The cohesive energy densities, ced, and the internal pressures, P, of aqueous methanol mixtures are calculated from literature data for the entire composition range over a temperature range of 273-473 K, at saturation pressures up to 373 K and at 7.0 MPa above this temperature. Ratios P/ced are measures of the "structuredness" of the studied fluids, and the small values noted signify "tight" structures, due to hydrogen bonding. The "tighter" the structure, the larger is the surface tension of the mixtures (at 298.15 and 323.15 K). This structural feature diminishes in intensity as the temperature and the methanol contents are increased, except in cold (≤298 K) and hot (≥423 K) water-rich mixtures. Under such exceptional conditions, the hydrogen-bonded structure of water is enhanced.