The stability of wetting films is important in many different industries and daily lives. As is well known, the stability is determined by the surface forces in the thin liquid film (TLF) of water confined between the solid/liquid and air/liquid interfaces. The surface forces in wetting films can be readily measured by approaching an air bubble toward a surface and monitoring the local curvature changes as reported previously. In the present work, we conducted the measurements with gold surfaces coated with self-assembled alkanethiols (C<sub>n</sub>SH) with n= 4 and 16 at different temperatures to determine the changes in Gibbs free energy (ΔG), entropy (ΔS), and enthalpy (ΔH) associated with film thinning and rupture. The free energy changes were determined using the Frumkin-Derjaguin isotherm based on the disjoining pressure isotherms Π(h) measured in the present work. The results showed that the instability of the wetting films formed on hydrophobic surfaces arises from the decreases in both enthalpy and entropy and that the process is driven by enthalpy changes in that |ΔH|&gt;|TΔS|. These findings are consistent with those reported earlier for the TLFs of water confined between hydrophobic gold and hydrophobic silica surfaces.

Thermodynamic analysis of the stability of the wetting films formed on hydrophobic gold surfaces

ACS Spring 2022

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