Abstract
Two oppositely charged surfactants in an aqueous solution interact with each other via electrostatic interactions and produce surfactant complexes—catanionics. However, their quantitative influence on the interfacial tension at the solution/air and solution/oil interfaces is still unknown. We have measured the interfacial tension of sodium dodecyl sul- phate (SDS) and dodecyltrimethylammonium bromide (DoTAB) aqueous mixtures using the du Nouy ring tensiom- eter and drop profile analysis tensiometry (PAT-1). For the oil phase, we used hexane. The obtained kinetic and equilibrium experimental results were fitted with the common theoretical Frumkin adsorption model. We found that SDS+DoTAB complexes show much higher surface activity than the single surfactants. At solution/air and solution/oil interfaces, SDS and DoTAB produce ion pairs with low water affinity and relatively low oil solubility. SDS+DoTAB partition coeffi- cient between hexane and water phases is 0.32. Such surfac- tant complexes with advanced surface characteristics may be beneficial in different industrial branches nowadays.
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