The long term objectives of the suspension rheology work of IFPRI were summarized by B. Yates in 1981 as: "The main long term aim is to be able to predict and manipulate the rheological behaviour of dispersed systems..."
The present project deals with two well defined but quite general aspects of this long term aim: 1) the development of qualitative insight and possibly quantitative predictions for the rheological behaviour of stable colloidal suspensions; 2) the generation of systematic data on weakly flocculated suspensions in order to elucidate the general pattern of their behaviour and to initiate their modelling.
The two classes of materials under consideration cover a large fraction of the industrial suspensions for which a specific rheology is required.
Systematic rheological measurements were performed on sterically stabilized colloidal suspensions. The following parameters were varied: particle size, concentration, temperature and the nature of the medium. The present set of data constitutes the most comprehensive study to date of the rheology of sterically stabilized systems. From the results a general procedure is derived which makes it possible to predict the rheological properties of sterically stabilized suspensions with a minimum number of experiments. Furthermore it is shown how oscillatory rheological measurements can be used to obtain information about suspension characteristics such as interparticle potential and particle diffusivity.
With respect to the second group, the weakly flocculated systems, two phenomena were investigated: yielding and thixotropy. The experiments on yielding indicate that stored energy models cannot be used here. A kinetically controlled mechanism must be introduced. Rheological and electric measurements were performed on thixotropic materials. Qualitative trends could be derived as well as a possible scheme for data reduction.
In conclusion it can be said that progress has been made along the following lines: 1) qualitative insight has been gained in the rheological behaviour of stable and flocculated suspensions; 2) experimental data have been collected which provide a basis for model assessment and model development; 3) practice oriented procedures have been suggested which can be used in industry for data reduction to predict rheological properties