The mechanical properties (rheology) of dispersed media such as liquid foams and emulsions is strongly affected by surface rheology. Indeed, when they consist of two (or more) fluid phases, deforming the material implies deforming the constitutive phases (bubbles, drops) and thus their interfaces.
The measurement of surface rheological properties is described by storage and loss moduli. In the case of a linear response to a sinusoidal deformation, the loss modulus is the product of the viscosity by the frequency. One of the difficulties of surface rheology measurements come from the fact that the adsorbed layers are usually rather compressible (at the difference of bulk fluids which are essentially incompressible), and both compression and shear parameters should be determined. This determination requires different type of rheometric instruments, for instance oscillating drops for the compression properties and oscillating bicones for the shear properties.[4] These two methods allow investigating the variation of the parameters upon the amplitude of the deformation. The responses of adsorbed layers to deformations are frequently non-linear, making this variation measurement relevant to rheological studies.
