Author(s)

Y. Pawar & K.J. Stebe

Abstract

The interface of a droplet in an extensional flow moves both tangentially and normally. When surfactants are adsorbed on the drop interface, Marangoni stresses, which resist tangential shear, and Marangoni elasticities, which resist surface dilatation, develop. In this paper, the dependence of these effects on surfactant physical chemistry, and their impact on drop deformation are probed. Repulsive or cohesive interactions between surfactant molecules change the surface equation of state which dictates the sensitivity of the surface tension to adsorbed surfactant. For example, cohesion decreases this sensitivity, favoring strong surface concentration gradients. Boundary Element results are presented for fluids of equal viscosities

Keywords