CONTACT ANGLES IN RELATION TO THE EFFECTS OF SOLIDS ON FILM AND FOAM STABILITY

It is well known that solid hydrophobic particles can reduce foaming, and this fact is used in formulating industrial antifoam preparations. The work to be described has centred on the acquisition of unambiguou s experimental data on well-defined systems in order to probe the role of the contact angle, theta, between particles and surfactant solutio ns in foam and single film breaking. It is expected that spherical par ticles and cylindrical rods will rupture soap films by a bridging-dewe tting mechanism for theta values of 90-degrees or more. Spherical glas s beads (diameters about 45mum) and cylindrical rods have been silanis ed to varying degrees to give a range of wettabilities. For theta grea ter-than-or-equal-to 90-degrees rods rapidly rupture single soap films into which they are incorporated. However, spherical particles maxima lly stabilise foams for theta = 90-degrees. Angles in excess of about 92-degrees are needed for effective foam reduction. The stabilising ef fect is attributed to collection of particles in the Plateau border re gions of the foams and the concomitant reduction in the rate of film d rainage.