Thermodynamics of solvophobic interaction between hydrophobic surfaces in ethanol

AFM surface force measurements were conducted in pure ethanol using gold surfaces hydrophobized with alkanethiols (CnSH) with n = 2-16. The forces measured at 5-35 °C were net attractive and became stronger with decreasing temperature and with increasing surface hydrophobicity. Thermodynamic analysis of the experimental data showed that the macroscopic solvophobic interactions were enthalpic but exhibited significant enthalpy-entropy compensations. The enthalpy decreases may represent the energy gained in forming H-bonded structures of ethanol, while the entropy decreases represent the thermodynamic costs for building structures. These results are consistent with those obtained previously in pure water.