Note Wagner’s draft report is essentially a final year annual report. He has been asked to include the earlier years work.
Executive Summary:
This project has the goal of providing experimental evidence for the influence of interparticle surface forces and hydrodynamic forces on the moderate to high shear rheological properties and shear stability of wet dispersions that span the colloidal to particulate range. In part I we demonstrate that true nanoparticle dispersions can be modeled and studied as colloidal dispersions. These results show that the continuum hypothesis of hydrodynamic interactions holds down to the nanometer scale. The research provides guidance on the formulation, rheological investigation, and modeling of nanoparticle dispersions. Part II completes a study on the effects of particle shape on colloid rheology. A model system of industrial relevance is characterized and studied. Rheology and neutron scattering under flow show that the mechanisms of reversible shear thickening in concentrated colloidal dispersions of ellipsoidal shaped particles are identical to that in colloidal dispersions of spherical particles. We show, however, that shear thickening appears at lower volume fractions in highly anisotropic particles and demonstrate a scaling that tracks the isotropic-nematic transition. Furthermore, the neutron scattering results demonstrate that shear thickening is not a consequence of flow-induced disorientation in these dispersions, dispelling that hypothesis and providing a quantitative means for predicting the onset of shear thickening in highly anisotropic dispersions. Part III provides a look forward for extending the research results obtained herein. It also includes results for clay dispersions that shows the universal nature of reversible shear thickening in spherical, prolate, and oblate particle dispersions.
The results of this body of work enable modeling and predicting that behavior of concentrated dispersions of colloidal and nano-sized particles that can be of assistance in formulating products and controlling processes involving dispersions.