AmericanChemicalSociety.com

Over the current period, we have made excellent progress in setting up a new set of experiments and measurements to understand how cohesive forces, particle and fluid inertia act in concert to determine the rigidity and dynamic properties of granular matter. As argued in the proposal, considerable amount of the world’s oil is located and mixed in with soil which makes fundamental understanding of granular-fluid properties important to understand.

In collaboration with post-doc Michael Berhanu, undergraduate students Darija Cosic and Michael Robitaille, we have made a system in which we examine the structure of cohesive granular matter with direct imaging. A novel feature of the experiment is that the volume fraction of the grains can be continuously varied while the attractive interaction strength is held constant. The structure is then analyzed from the particle position extracted from the images, using measures including the number of contacts, cluster size, radial correlation function, and Voronoi volume fraction distribution.

We find clear signatures of differences between cohesive and non-cohesive particles using these measures. In particular the free volume distribution is different from a Gamma distribution and indicated wider distributions, which go to the Gamma distribution at highest volume fractions and compression. These measures also show that the connectivity transition occurs at lower volume fraction, and the rigidity at distinct and higher volume fraction, further it shows that new models are required to capture the observed distributions.

We are in the final stages of refining our measurements, and then we plan to write manuscripts reporting our results in the coming year.