Surfactant diffusivity measurement by transient capillary rise

Abstract

A new method, transient capillary rise, is proposed to determine surfactant diffusivity. Compared to previously available tecniques such as Taylor dispersion, the new technique is inexpensive, and the diffusivity can be obtained from a simple measurement. The concept of the proposed method is based on the fact that the height of liquid solution in a capillary tube rises as surfactant concentration decreases. The mathematical model was developed using the theory of capillary force, Gibbs plot (surface tension versus concentration) and mass transport of the surfactant in the tube. If the theory holds, it should be possible to determine surfactant diffusivity by fitting a mathematical model to the change of liquid height as a function of time. In the present work, the validity of the method was tested by comparing the diffusivity of sodium dodecyl sulfate with literature values. The results showed that the diffusivity values obtained from this work are higher than values obtained by the Taylor dispersion method.