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 fi lms. The contact angles are calculated for aqueous solutions of electr olytes of low concentration on quartz surface, taking into account for ces of molecular repulsion, electrostatic attraction and structural fo rces. A high degree of surface hydrophilicity may be attained under th e predominant action of repulsive structural forces. Large contact ang les are caused by the predominant action of hydrophobic attraction for ces and/or electrostatic attraction forces acting between two opposite ly charged film interfaces. At a moderate degree of hydrophilicity, in the range of contact angles from 10-15 degrees to 50-60 degrees, it i s sufficient to take into account the molecular and electrostatic forc es only. This determines the region of applicability of the DLVO theor y. The parameters of the short-range hydrophobic forces seem to be the same in wetting films and in water interlayers between two hydrophobi c surfaces.