Capillary rise of surfactant solutions

The capillary flow of surfactant solutions in hydrophobic and hydrophilic c apillaries has been studied. The results obtained are discussed in the ligh t of surface tension relaxation and adsorption phenomena. Modes of surfacta nt transport and effects of surfactant adsorption, aggregation, and monomer -micelle interconversion on the capillary rise dynamics are further analyze d in the framework of a theoretical model. This provides a self-consistent and quantitatively correct picture of the experimental results. In the case of hydrophobic capillaries, two limiting types of dynamic behavior are ads orption-controlled rise and diffusion-controlled rise. In some cases, slow relaxation of adsorbed layers at the liquid/solid interface can cause a dri ft of the rise height over a long time under quasi-equilibrium conditions. A slow relaxation, as compared to the capillary rise rate, of the liquid/va por interface may also produce a maximum in the rise vs. time curve. This b ehavior was, for instance, seen for a surfactant solution penetrating into a hydrophilic capillary.