Retardation of Droplet Motion by Surfactant. Part 2. Numerical Solutions for Exterior Diffusion, Surface Diffusion, and Adsorption Kinetics

The coupled fluid mechanics and mass transfer problems for the retardation by surfactant of an essentially spherical droplet in creeping flow are solved simultaneously. The mass transfer mechanisms of diffusion in the exterior liquid, surface diffusion, and adsorption kinetics are treated separately. No assumptions are made concerning the form of the velocity profile. The solutions are obtained by collocation methods with Newton iteration. The velocity profile and concentration distribution are improved simultaneously, not alternately. The numerical results reveal as limiting cases the uniformly retarded and stagnant cap interfacial velocity profiles considered previously.