Rheology of Concentrated Colloidal Dispersions

EXECUTIVE SUMMARY

IFPRI funding enabled us to consolidate and complete work on the rheology of stable, phase separated, and flocculated dispersions initiated with partial funding from several other sources. While not attaining the predictive level initially anticipated, the effort has furthered the qualitative understanding connecting interparticle forces to specific rheological responses.

The work has the following components:

1. The development of a non-equilibrium statistical mechanics approach for stable dispersions provides the framework for quantitative predictions of the low shear viscosity and linear viscoelastic properties as functions of the particle size and volume fraction and the interparticle potential. Though potentially powerful, the approach is currently limited by the lack of a tractable approximation for many-body hydrodynamic interactions.
2. The effective medium and self-consistent field approximations for the elasticity and plasticity, respectively, of flocculated suspensions capture the sensitivity to volume fraction due to the network structure and the breakup of the network into floes under shear. The predictions should be useful in correlating data, but are not yet fully predictive.
3. The correlation of data for model systems with well characterized particle sizes and interaction potentials demonstrates the value the qualitative understanding gained from fundamental approaches even when not completely predictive.