ABSTRACT
This chapter considers the kinetics of spreading of surfactant solutions over hydrophobic, porous substrates and over thin aqueous layers. It investigates the kinetics of the capillary imbibition of aqueous surfactant solutions into hydrophobic capillaries. The spreading of surfactant solutions is a very special case of partial wetting: the static receding contact angle is zero, which is the same as in the case complete wetting. Pure water does not penetrate spontaneously into a hydrophobized quartz capillary; however, surfactant solutions do penetrate spontaneously, and the penetration rate depends on the concentration of surfactant. The concentration of surfactant changes considerably only in close proximity to the moving meniscus. Surfactant adsorption onto solid–liquid and liquid–vapor interfaces changes the corresponding interfacial tensions. The spreading of surfactants makes the water flow away from the initial location of the drop thus creating a depression where only a thin film of liquid subsists.
