Surface dilational properties of mixed sodium dodecyl sulfate/dodecanol solutions

The surface dilatational properties of aqueous solutions of sodium dodecyl sulfate (SDS) and n-dodecanol areinvestigated in the frequency range 15/f5/500 Hz using the oscillating bubble method. The results demonstrate that apure dodecanol solution has an elastic surface without viscous effect whereas the surface of a SDS solution withoutadded dodecanol exhibits a strong viscoelastic behavior. Mixtures show graduated properties. The time behavior oftheir surface dilatational moduli demonstrates that dodecanol molecules drive the SDS molecules slowly out of thesurface. Therefore, the known one-component model describing the surface dilatational modulus can be used also forthese mixtures. A simple theoretical consideration explains this effect.