COMPOSITION AND ELASTICITY OF THIN LIQUID FILMS

Gibbs elasticities were measured of thin liquid films drawn from solutions containing sodium decanesulfonate and varying amounts of dodecanol pentaethyleneglycol ether. The concentration ratio of the two surfactants was about 105. The elasticity increases strongly with increasing concentration of the nonionic surfactant. Surface tension was measured simultaneously with the elasticity. Analysis of the results shows that (i) the concentration of the nonionic surfactant is appreciably lower in the film liquid than in the bulk solution; (ii) the increased film elasticity is due to displacement of ionic surfactant by the nonionic compound at the surface.