Relation between the Variation of the Contact Angle and the Adhesion Force between Silica Surfaces

Adhesion force and contact angle measurements between an aqueous solution of the nonionic surfactant TN 101 and silica surface have been studied. The variation of the contact angle is a function of the adsorption of the surfactant at the liquid–vapor, solid–liquid, and solid–vapor interfaces. The contact angle is maximum well below the cmc, when a monolayer of surfactant is formed at the silica surface. To this maximum contact angle corresponds a maximum adhesion force between the silica surfaces. This force is due to the hydrophobic interaction between the alkyl chain of the surfactant adsorbed at the silica surface.