Rheology of a dilute emulsion of surfactant-covered spherical drops

The rheology of a diluted emulsion of surfactant-covered spherical drops has been investigated. A diluted film of insoluble surfactant is assumed. A matrix formulation of the problem is derived and analyzed by perturbation expansions for low- and high-shear rates, and for high-viscosity drops; the high-viscosity expansion converges rapidly for a wide range of parameters. Our theory provides a quantitative description of shear thinning and normal stress differences that occur as a result of surfactant redistribution. (C) 2000 Elsevier Science B.V. All rights reserved.