Surfactant diffusivity measurement by transient capillary rise

Abstract

Surfactant diffusivity measurements are of great interest, in part, due to its importance in many aspects like cleaning processes and textile industries (Rosen 1989). Presently, the most commonly used technique to determine surfactant diffusivity is the Taylor dispersion (peak-broadening) method (Pratt and wakeham 1974). Accuracy of the method comes with expensive equipment and complex analysis. Here, a new and simple method to obtain surfactant diffusivity is proposed based on the transient capillary rise. The method flooows the change of surfactant concentration through surface tension measurements in a capillary tube. The change is then correlated to a mass balance equation, in which surfactant diffusivity is embedded. Sodium dodecyl sulfate (SDS), Tetradecyl trimethly ammonium bromide (CTAB), and Octylphenol ethylene oxide condensate (Triton X-100) as an anionic, cationic and nonionic surfactant respectively were used to test the validity of the proposed method. The transient capillary rise method can readily be used to obtain SDS and Triton X-100 diffusivity with a small deviation from that obtained from the Taylor dispersion method. As the proposed method meeds the change of surface tension data to obtain diffusivity and the surface tension of CTAB from the capillary tube method tends to be constant, it is not applicable for CTAB diffusivity measurements at any concentration.