Zusammenfassung
The surface dilatational modulus E is a fundamental system parameter of aqueous surfactant solutions which plays an important role in the physic of foams. In this contribution, we study the influence of highly charged Cerium-ions (Ce4+)-on the surface dilatational modulus E of aqueous sodium dodecyl sulfate (SDS) solutions. The E-modulus has been determined at two concentrations below the ...
Zusammenfassung
The surface dilatational modulus E is a fundamental system parameter of aqueous surfactant solutions which plays an important role in the physic of foams. In this contribution, we study the influence of highly charged Cerium-ions (Ce4+)-on the surface dilatational modulus E of aqueous sodium dodecyl sulfate (SDS) solutions. The E-modulus has been determined at two concentrations below the critical micellar concentration (cmc) in the frequency range from 3 Hz to 500 Hz using the oscillating bubble technique. The presence of Ce4+-ions increases the surface activity of the surfactant leading to a shift of the equilibrium surface tension isotherm to lower concentrations. The cmc is reduced to 2 x 10(-3) mol L-1. Adsorption layers of aqueous SDS solutions exhibit a surface visco-elastic behavior. The magnitude and the phase of the complex dilatational modulus E increase in a continuous fashion with the frequency indicating a dissipative process within the adsorption layer. The presence of the electrolyte modifies the frequency characteristics of the complex modulus towards the features of a surface elastic system. Furthermore there are pronounced changes in the stability of the corresponding foams. The lifetime of wet foam lamella is significantly reduced by the presence of the Ce4+-ions. The results provide evidence for the decisive impact of surface visco-elastic properties on foam stability of aqueous surfactant solutions. (C) 2016 Elsevier B.V. All rights reserved.
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