Rheological behavior of microemulsions.

We study the stationary and transient behaviors of a microemulsion phase subjected to a shear flow. The system is described by a diffusion-convective equation that generalizes the usual Cahn-Hilliard equation. Nonlinear terms are treated in a self-consistent approximation. Shear, first and second normal stresses are calculated as momenta of the structure factor. Shear thinning is observed in stationary conditions. After a Newtonian regime at small values of the shear rate, the excess viscosity decreases when the shear rate becomes of the order of the inverse of the relaxation time of the system without flow. In transient regimes, when the flow is applied starting from a quiescent state, we find that the shear stress reaches a maximum before decreasing to a constant value.