THE RELATION BETWEEN COLLOID STABILITY AND WETTING

Surface forces acting between colloidal particles and in wetting films are considered. Wetting films, as distinct from colloids, represent a nonsymmetrical system bounded by a solid and a gas phase. The electrical potentials of solid-liquid and liquid-air interfaces can be different not only in value, but sometimes also in the sign causing the forces of electrostatic attraction. Particular attention has been given to the effect of structural forces. They play a dominant role in the region of contact angles at theta < 20 degrees (hydrophilic repulsion forces) and at a > 40 degrees (hydrophobic attraction forces). The intermediate region corresponds to the field of application of the DLVO theory. The short-range hydrophobic forces in wetting films of water seem to be the same as in water interlayers between two hydrophobic surfaces. This may be explained by considering unstable wetting films to be disposed between two hydrophobic surfaces: the hydrophobic solid substrate and the hydrophobic water-air interface. It is suggested that lyophobic attraction forces can also exist in other polar liquids bounded by two low-energy nonwetting surfaces. (C) 1995 Academic Press Inc.