Hydrophobic interaction in water-ethanol mixtures

The solubility, free energy, entropy, and enthalpy of solutions of methane and ethane were determined in various mixtures of water and ethanol. The hydrophobic interaction for the pair methane-methane was computed, in these mixtures, using an approximate expression derived previously. Also the entropy and the enthalpy associated with the hydrophobic interaction were evaluated from the experimental data. The main finding is the steep decrease in the strength of the hydrophobic interaction as the mixture becomes richer in alcohol. The variation of the corresponding entropy and enthalpy also shows an abrupt change at the composition of x_ethanol≈0.2. Some interpretations of these findings in terms of structural changes in the solvent are discussed.