THE SPREADING OF AQUEOUS SURFACTANT SOLUTIONS ON GLASS

Abstract

An investigation of the spreading behavior of drops of a number of aqueous anionic, cationic and non-ionic surfactant solutions has demonstrated, for the first-time, spreading to a maximum solid-solution contact area, and then contraction to a smaller final size. The nature and kinetics of the spreading and contraction are shown to be dependent on the type and concentration of the surfactant. Generally, the maximum contact area decreases with increasing surfactant concentration, to a minimum (or no spreading) in the vicinity of the CMC. Above the CMC, anionic and nonionic surfactant solutions spread with peripheral fingering, followed by contraction, while cationic surfactant solutions do not spread at these concentrations. The results are explained in terms of the thin primary film spreading ahead of the drop.