Hydrophobic interaction in water-p-dioxane mixtures

The solubility, standard free energy, entropy, and enthalpy of solution of methane and ethane were determined in various mixtures of water and 1,4-dioxane. The strength of the hydrophobic interaction as well as its temperature dependence were estimated from the experimental data. It is found that the hydrophobic interaction first increases upon the addition of dioxane to pure water. At higher concentration of dioxane the hydrophobic interaction gradually weakens until it reaches its relatively low value for pure dioxane. The entropy and the enthalpy changes accompanying the process of hydrophobic interaction exhibit a more abrupt behavior as a function of the mole fraction of dioxane. Namely, the anomalously large and positive values of the entropy and the enthalpy changes decrease steeply in the range of 0 ≤ x_dioxane ≲ 0.25, and then attain almost constant values.