Comment on "reevaluation in interpretation of hydrophobicity by scaled particle theory"

In a letter, Kodaka tried to provide an interpretation of the results from scaled particle theory (SPT) using calculations different from the usual ones. Inspection of the SPT equation for ΔGc indicated that the latter, at a given temperature for a given cavity diameter, is a function of the size of the solvent molecules, σ, and the volume packing density of the solvent, ξ = πσ3NA/6ν, where ν is the molar volume of the solvent itself. Graziano suggested a possible step-by-step way to analyze Kodaka's arguments and to point out the conceptual flaws. The values of σ, ν, ξ, ΔvapH, and cohesive energy density at 25°C for several liquids, e.g., n-hexane, n-heptane, cyclohexane, benzene, toluene, CCl4, CS2, acetone, H2O, methanol, ethanol, cyclohexanol, and ethylene glycol, were collected. The present analysis confirmed the assertion that σ and ξ were the correct variables to use in analyzing the SPT formula of ΔGc because they represent the length scale and the occupied space of the liquid, respectively. It was re-stated that ΔGc was larger in water than in other common solvents due to the smallness of the water molecules themselves, as originally claimed by Lucas et al.