Incorporating granules and suspensions into a unified phase diagram

When baking, adding a small amount of milk to flour leads to small, dry, rough flakes of dough, while adding a larger amount transforms the mixture into a wet, dense mass. This transition exemplifies the difference between granules and dense suspensions, and understanding the link between the two is important for key industrial processes like food, pharmaceuticals, and construction.

Hodgson et al. combined a glass powder with varying amounts of liquid and under two types of mixing — high and low stress — to create a liquid incorporation phase diagram. The result maps out when granulation occurs and may improve the speed and cost of granule design.

At low solid loadings, which include more liquid, the samples remained a flowing suspension at both high and low stress. At very high solid loadings, the samples formed granules no matter the stress. For mixtures in between, low stress led to a flowing state, while high stress resulted in granules.

For samples in the flowing state, the team measured the viscosity as a function of applied stress. The samples exhibited shear thickening, increasing their viscosity after the stress hit a critical point. By plotting viscosity as a function of solid loading, they determined that samples under high stress diverged from a flowing suspension at lower solid fractions.

“By situating these two observations on the same plot for the first time, we were able to generate a ‘liquid incorporation phase diagram’ which shows, unambiguously, that granulation and shear-induced jamming are linked by the same underlying physics,” said author Daniel Hodgson. “The main takeaway is that dense suspension and granulation communities can learn from each other.”

Source: “Granulation and suspension rheology: a unified treatment,” by Daniel J. M. Hodgson, Michiel Hermes, Elena Blanco, and Wilson C. K. Poon, Journal of Rheology (2022). The article can be accessed at https://doi.org/10.1122/8.0000515 .