Limitation of the Young-Dupre equation in the analysis of adhesion forces involving surfactant solutions

The atomic Force microscope was used to measure adhesion forces between pol yethylene particles, serving as model oil droplets. and mineral substrates (fluorite and quartz) in aqueous solutions of ethoxylated alcohols. Also. c ontact angles were measured in the kerosene ethoxylated alcohol solution-mi neral systems. Correlations obtained between adhesion and surfactant concen tration for the polyethylene -aqueous solution-quartz system differs signif icantly from those predicted by the Young-Dupre equation For the kerosene-a queous solution-quartz system. Interactions, characteristic for such aqueou s systems, which contribute to the pull-off forces measured by atomic force microscopy are nor included in the Young-Dupre equation, and are primarily responsible for the inconsistency in the adhesion versus surfactant concen tration relationship obtained from contact angle measurements.