RHEOLOGY OF CONCENTRATED DISPERSED SYSTEMS IN A LOW-MOLECULAR-WEIGHT MATRIX

The objective of this paper is to provide a complete theoretical and experimental study of shear rheology for concentrated dispersed systems in low molecular weight matrices. A new theoretical approach based on qualitative microstructural physics and thermodynamical arguments is developed which considers flow, elastic deformations, ruptures and restorations of flocs. The approach was developed to study steady and transient phenomena and has predicted very different behaviours for various systems; one of them was a non-monotonic flow curve. The most remarkable feature of the theoretical model is that it contains no mathematical yield criterion but predicts anisotropic yield values with continuous transition from solid state to flow as a bifurcation. A complete set of experiments in simple shearing was carried out for two different dispersed systems: a granular grease and a water-clay platelet mixture. Also some disturbing phenomena were observed and experimental techniques were developed which made it possible to obtain reliable results. Additionally the clay-water system exhibited a minimum in the flow curve, and all the characteristics peculiar to the evolution from solid state to flow, as predicted by the theory. Despite the short time scale of transition phenomena for the materials tested, the general comparison of experimental results with theory showed good agreement.