ON THE MODELING OF THE RHEOLOGICAL BEHAVIOR OF BENTONITE DISPERSIONS IN POLYMER SOLUTIONS

Bentonite dispersions in polymer solutions may behave as gel like materials. Under stress, the structure formed at rest is progressively destroyed and a solid-liquid transition occurs. The rheological characterization of such kind of systems is often done by applying stress ramps of the sample. A simple Herschel-Bulkley equation is not convenient to fit the answer of the material to the ramp since it does not take in account the effect of time. The models for yield stress fluids involving two viscosity levels are not convenient too since they don't take in account the elastic behavior at low stresses. We propose in this paper two equations in order to determine some parameters characterizing the rheological behavior of such systems. The results obtained both in oscillatory and permanent shear are compared according to Winter's representation and a rescaling of the complex modulus is proposed to superimposed the data in the solid/liquid transition region.