Clustering and Charging in Granular Flows

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****Technical Abstract****The project employs freefalling streams of granular material to investigate particle interactions and aggregation in two closely coupled research efforts. First, tribocharging of same-material grains is investigated, a phenomenon of high significance scientifically as well as for applications, whose detailed mechanism is still being debated. Tracking tribocharged grains in dilute granular streams as they enter a region of uniform electric field makes it possible to collect the full statistical distribution of grain charge and its dependence on grain size. Results from this work will not only provide a better understanding of the fundamental mechanism giving rise to tribocharging, but also new insights that can help to control it. Second, by increasing the particle density inside the stream, the probability of particle-particle interactions can be increased systematically. This makes it possible to induce particle capture processes and follow in-situ the subsequent agglomeration into larger clusters, providing a first detailed look at the interplay of short-range cohesion and longer-range electrostatic forces. The project will train a PhD student and a postdoc in forefront materials research, and it includes the active participation of undergraduates. The research component of the project will be integrated with a multi-faceted set of education and outreach activities, including activities with the nearby Chicago Museum of Science and Industry.****Non-Technical Abstract****Granular materials are large aggregates of small particles. Within condensed matter physics and materials science, these materials pose a challenge because their complex behavior falls outside the established predictions for ordinary solids or liquids. At the same time, the handling, storage and transport of granular materials are critical to our economy, and improved knowledge opens up new opportunities for better control. The objective of this project is to establish a fundamental understanding of how particle collisions can drive agglomeration into particle clusters and what role electrostatic charging plays in this process. The research is centered around a unique experimental facility in which freely falling streams of particles are imaged and tracked with very high spatial and temporal precision. Better control of particle clustering and charging will impact areas from physics to engineering to environmental sciences. The clustering of charged particles is also relevant to the formation of aggregates in interstellar dust. The project will train a PhD student and a postdoc in forefront materials research, and it includes the active participation of undergraduates. The research will be integrated with a multi-faceted set of education and outreach activities, including activities with the nearby Chicago Museum of Science and Industry.