Cube vs. sphere: A rheological look at cubic particle suspensions
Cube vs. sphere: A rheological look at cubic particle suspensions lead image
Particle suspension flow properties make for a broad and consequential area of scientific inquiry, with almost all such studies — theoretical, numerical, or experimental — focusing on spherical particles. Yet, in many real-world fluid suspensions, including fresh concrete, rocket fuels, chocolate, and even volcanic lava, particle shapes are more cubic than spherical.
After photolithographically fabricating cubic particles, d’Ambrosio et al. dispersed them in mineral oil and conducted rheometric experiments to measure two key properties: viscosity and particle pressure, a less familiar property.
“When the suspension is sheared, particles move at different speeds and collide, causing deviation from their trajectories,” said author Elizabeth Lemaire. “Repeated collisions generate an internal pressure, somewhat analogous to gas pressure, but here it depends not on temperature, but shear intensity.”
The researchers measured viscosity conventionally with a rheometer. For particle pressure, they performed original resuspension experiments, placing the cubes, which are denser than the surrounding liquid, in a vertical cylindrical rheometer and shearing the system by rotating the inner cylinder. The height of the expanded sediment at the bottom provided for an estimate of particle pressure.
“Suspensions of cubes are much more viscous than those of spheres at the same concentration, and this difference becomes more pronounced as the solid fraction increases,” said Lemaire. “Similarly, at given concentrations, cubic suspensions generate much higher particle pressures, leading to stronger resuspension.”
However, compared at their respective “jamming fractions” — points at which their viscosities rise enough to stop suspension flow — cubes and spheres behave very similarly.
“This suggests both viscosity and particle pressure follow nearly universal laws depending on how close the system is to jamming, regardless of particle shape,” said Lemaire.
Source: “Rheology of suspensions of cubic particles,” by E. d’Ambrosio, D. Gilbert, F. Blanc, C. Cohen, and E. Lemaire, Journal of Rheology (2025). The article can be accessed at https://doi.org/10.1122/8.0001045 .
