THE INFLUENCE OF SURFACTANTS ON THE HYDRODYNAMICS OF SURFACE WETTING

The hydrodynamic model of steady wetting developed by Boender et al. [ Boender, W., Chesters, A.K.,van der Zanden, A.J.J., 1991. Int. I. Mult iphase Flow 17, 661-676] is extended to include the effect of a (non-i onic) surfactant. The approximation that the meniscus inclination beco mes equal to the static contact angle at a distance from the solid of the order of a molecular dimension is extended to take account of the local surfactant concentration, making use of Young's law. A second in ner boundary condition, provided by a surfactant balance at the contac t line, places a restriction on the speed at which the interface is sh ed, leading to surfactant accumulation and partial or almost total imm obilization of the interface which reduces the wetting speed. Under ce rtain conditions this immobilization is self-stabilizing, leading to h ysteresis effects. (C) 1998 Elsevier Science B.V. All rights reserved.