Thermal-to-athermal systems

It’s common knowledge that sand sinks in water. However if those sand grains are ground up further to smaller sizes they no longer sink and exhibit Brownian motion. This simple example demonstrates that the motion of particles suspended in solution is dictated by their size. Small particles belong to the thermal (colloidal) regime where Brownian motion is dominant. As particle size increases their motion becomes more dominated by gravity and they cross into the athermal (granular) regime. The Péclet number is a measure of which regime the particle is in and therefore describes the balance between gravitational and Brownian motion of a particle.

Previous work has shown how translational dynamics change as a function of Péclet number e.g. the effect of changing Péclet number on translational coupling in sedimentation. However the effect on rotational dynamics remains unexplored. Using the OCULI particles developed by our group we investigate the rotational how rotational dynamics change as we cross from one realm into another. We are also particularly interested in the onset of friction in particulate materials, and use our OCULI particles to probe this.