Dynamic and Rheological Properties of Span 80 at Liquid–Liquid Interfaces

The adsorption characteristics of Span 80 at liquid/liquid interfaces were investigated. The equilibrium interfacial tension values were successfully fitted with a Langmuir isotherm resulting in the determination of a mean molecular area from 25 to 35 angstrom(2)/mol. The measured interfacial tension values and deduced adsorption parameters depend on the experimental technique used to obtain them, either Du Nouy ring or profile analysis tensiometry. Two possible explanations to such phenomenon are provided. Adsorption kinetics of Span 80 at liquid/liquid interfaces were studied, and it was concluded that the diffusion of Span 80 molecules from the bulk is the rate determining step of the adsorption. Finally the interfacial rheology properties were investigated and compared to the Lucassen-van den Tempel model. A good match was obtained when the isotherm parameters determined by profile analysis tensiometry were used.