shutterstock.com/Gabor BalazsMany products (or product precursors) in the paint, personal care, cleaning, coatings and food areas, etc., contain large amounts of finely divided solid particulate material dispersed in a liquid matrix. The amount, shape, size distribution and interaction between these suspended particles and the surrounding liquid phase play a major part in determining overall product flow properties.
The physical state of the particles in the finished product may result from a combination of ingredients – solid and liquid, or else as a result of the particular process route used, i.e., crystallization or milling.
The rheology of any such particle suspension arises from the disturbance of the continuous-phase fluid flow, with any deviation of flow lines resulting in the extra dissipation of energy, giving an increased viscosity. A complicated interaction between the flow - which seeks to align and order the particles – colloidal interactions, which cause particles to be attracted or repelled from each other, and Brownian motion, which seeks to randomize the particles in space, all interact to give the rheology.
Measuring the rheology of particulate suspensions has its own challenges, in terms of instrument artefacts due to the interaction of the particles with the rheometer walls, and the creation of a meaningful choice of shear rates, etc.
In this guest webinar, Professor Howard Barnes aims to provide a simple understanding of this situation, and highlights how to bring about a more desirable rheology when necessary. This is important since the rheology of such products plays an important part in the technical behaviour as well as the aesthetic appeal of the product to the user. Examples from a number of product areas will be given.