Читать книгу The Rheology Handbook - Thomas Mezger - Страница 87

Rotation of a particle occurs clockwise when using a Two-Plates model with a fixed lower plate and the upper plate moving to the right. Cube-shaped particles are requiring of course more space when rotating compared to the state-at-rest. As a consequence, between the particles there is less free volume left for the dispersion liquid. On the other hand, spherical particles require the same amount of volume when rotating or when at rest; these kinds of dispersions are less likely to show shear-thickening. A material’s ability to flow can be improved by increasing the amount of free volume available between the particles. This can be achieved by changing the shape of the particles, – and of course also by adding more dispersion liquid.

Note 1: Droplet subdivision when testing emulsions

When shearing emulsions, with increasing shear rates sometimes sloping up of the viscosity curve can be observed. This may be assumed to be an indication of shear-thickening behavior. However, this effect is often occurring due to a reduction of the average droplet size, caused by droplet subdivision during a continued dispersing process due to the shear forces. Here, corresponding increase of the volume-specific surface (which is the ratio of droplet surface and droplet volume) and, as a consequence, the resulting increase in the interactions between the now smaller droplets may lead to higher values of the flow resistance (more on emulsions: see also Chapter 9.1.2 and [3.21] [3.22].