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Surface rheology is a description of the rheological properties of a free surface. When perfectly pure, the interface between fluids usually displays only surface tension. But when surfactants are adsorbed on the interface, because they lower the surface tension, the stress within the interface is affected by the flow for several reasons.
- Change in the surface concentration of surfactants when the in-plane flow tends to alter the surface area of the interface (Gibbs' elasticity).
- Adsorption/desorption of the surfactants to/from the interface.
Importance of surface rheology
The mechanical properties (rheology) of dispersed media such as liquid foams and emulsions is strongly affected by surface rheology. Indeed, when, they consist in two (or more) fluid phases, deforming the material implies deforming the constitutive phases (bubbles, drops) and thus their interfaces.