The temperature-dependence of the dynamic contact angle.

The MKT successfully accounts for the temperature-dependence of the dynamic contact angle, yielding rational values for key parameters including the activation free energy of wetting. Arrhenius-like behavior is also demonstrated. These results would appear to confirm that, at the molecular-scale, dynamic wetting is a thermally-activated rate process and that the influence of temperature is not restricted simply to its effect on surface tension and viscosity. The data show a discontinuity at dynamic contact angles between 60° and 90° that implies a velocity-dependent change in the wetting mechanism. We attribute this to the chemical heterogeneity of the PET surface, which contains both polar and non-polar groups. The parameters obtained by applying the MKT suggest that the interactions of DBP with these groups determine, respectively, the dynamics observed below and above the transition. The sum of the activation free energies of wetting on either side of the transition is close to the total thermodynamic work of adhesion of DBP to PET.