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Diffusivity Measurements of Solutes Impacting Interfacial Tension

Chernyshev, Vasiliy S., Skliar, Mikhail
Industrial & Engineering Chemistry Research 2015 v.54 no.16 pp. 4535-4544
absorption, active ingredients, air, diffusivity, engineering, guidelines, laboratory equipment, liquids, models, solutes, surface tension, surfactants, vapors
We propose a method for measuring gas and liquid diffusivities of surface active solutes based on the measurements of dynamic interfacial tension. The selection of the experimental system needed to achieve accurate diffusivity estimation and, particularly, the selection of the complementary fluid to create the interface sensitive to the solute concentration are emphasized. The method is applicable to solutes beyond traditional liquid-phase surfactants and is demonstrated by estimating diffusivities of several vapors in air. Though the method allows for surface active compounds that traverse the interface, the procedure for estimating diffusion coefficients is particularly simple in cases when the solute is insoluble in the complementary fluid and when its flux across the interface is small. It was shown that by adding surfactants to the complementary fluid, it may be possible to reduce the flux of the solute across the interface by increasing the resistance to cross-interfacial transport and to identify diffusivities with higher accuracy based on simple data analysis. The improved accuracy is also achieved when the diffusivity is identified based on models that, when appropriate, account for the absorption of the solute into the complementary fluid. The developed method is simple, rapid, suitable for many applications, and often can be implemented using only basic laboratory equipment. We discuss its advantages, limitations, and provide user guidelines for its implementation.