Prediction of contact angles on the basis of the Frumkin-Derjaguin approach

The Frumkin-Derjaguin approach was used for the calculation of contact angles on the basis of isotherms of disjoining pressure of wetting films. The contact angles are calculated for a queous solutions of electrolytes of low concentration on quartz surface, taking into account forces of molecular repulsion, electrostatic attraction and structural forces. A high degree of surface hydrophilicity may be attained under the predominant action of repulsive structural forces. Large contact angles are caused by the predominant action of hydrophobic attraction forces and/or electrostatic attraction forces acting between two oppositely charged film interfaces. At a moderate degree of hydrophilicity, in the range of contact angles from 10–15° to 50–60°, it is sufficient to take into account the molecular and electrostatic forces only. This determines the region of applicability of the DLVO theory. The parameters of the short-range hydrophobic forces seem to be the same in wetting films and in water interlayers between two hydrophobic surfaces.