Rheological Behavior of Microemulsions

TL;DR

This paper investigates the rheological properties of microemulsions under shear flow, revealing shear thinning behavior and transient stress responses using a generalized diffusion-convective model.

Contribution

It introduces a self-consistent approach to analyze the non-linear rheological behavior of microemulsions under shear, extending the classical Cahn-Hilliard framework.

Findings

Shear thinning observed in stationary conditions.

Shear stress peaks before reaching steady state.

Excess viscosity decreases at high shear rates.

Abstract

We study the stationary and transient behaviors of the microemulsion phase subjected to a shear flow. The system is described by a diffusion-convective equation which generalizes the usual Cahn-Hilliard equation. Non-linear 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.