Nonlinear rheology of complex fluid–fluid interfaces

Fluid–fluid interfaces stabilized by proteins, protein aggregates, polymers, or colloidal particles, tend to have a complex microstructure. Their response to an applied deformation is often highly nonlinear, even at small deformation (rates). The nonlinearity of the response is a result of changes in the interfacial microstructure. Most of the studies on interfacial rheology of complex interfaces currently available in the scientific literature, focus on the linear response regime. Since multiphase systems such as emulsions or foam are routinely exposed to large and fast deformations, characterization of the nonlinear response of complex interfaces is highly relevant. In this paper we review the recent work on nonlinear rheology of complex interfaces, both in shear and dilatational deformations. We also discuss several methods currently available for analyzing nonlinear interfacial rheology data, and recent progress in modeling nonlinear interfacial rheology, using nonequilibrium thermodynamic frameworks.