Freely-Falling Granular Powder Streams as Sensitive Probes of Interparticle Forces

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0933242JaegerA better understanding of the behavior of powders is becoming increasingly important as industrial processes require smaller and smaller particle sizes. In addition, there is a growing realization that the existence of fines even in nominally larger sized powders critically affects their flowability. What makes dense granular powder flows particularly challenging is the multitude of interparticle forces that are at work simultaneously and the range of size scales involved, down to nanoscale particle surface roughness. In this regard, freely falling streams of powder offer special opportunities to investigate particle particle as well as particle-gas interactions because they make it possible to observe very small interparticle forces directly.Intellectual Merit. Changes in the free falling stream profile and, in particular, the break up of the stream into particle clusters can serve as macroscopic signatures and sensitive diagnostics of microscopic, grain-scale interactions. The research involves a unique experimental facility designed to track the evolution of dense granular powder streams over two meters of free fall, using a high speed video camera falling alongside the particulate material. The combination of imaging in the co-moving frame with extensive computer modeling and with characterization of grain surfaces by atomic force microscopy and scanning electron microscopy is used to establish a quantitative connection between the overall stream properties and their dependence on various types of cohesive particle-particle interactions, including capillary, van der Waals and electrostatic forces.Broader Impact: In addition to the industrial and economic value associated with the proper control of particulate matter, the study of granular materials provides insights into fundamental, crosscutting scientific issues across a wide range of science and engineering disciplines. The research will train graduate students in key aspects of particulate matter and multi phase flow research, and it includes the active participation of a large and diverse group of undergraduates as well as a close collaboration with an industrial partner. 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.