Clustering and Charging in Granular Flows

*技术摘要*该项目使用自由落下的颗粒状物质流来研究两个紧密耦合的研究工作中的粒子相互作用和聚集。首先，研究了同种材料颗粒的摩擦带电现象，这一现象在科学上和应用上都具有很高的意义，但其具体机理仍在争论中。当稀薄颗粒流中的摩擦带电颗粒进入均匀电场区域时，跟踪它们可以收集颗粒电荷的全部统计分布及其与颗粒尺寸的关系。这项工作的结果不仅将为更好地理解引起摩擦带电的基本机制提供更好的理解，而且还将提供有助于控制摩擦带电的新见解。其次，通过增加流内的颗粒密度，可以系统地增加颗粒-颗粒相互作用的几率。这使得有可能诱导粒子捕获过程，并在原位跟随随后的凝聚成更大的团簇，提供了第一个详细的观察短程凝聚力和长程静电力的相互作用。该项目将培养一名博士生和一名博士后从事前沿材料研究，并包括本科生的积极参与。该项目的研究部分将与一系列多方面的教育和外联活动相结合，包括与附近的芝加哥科学和工业博物馆的活动。*非技术摘要*颗粒状材料是小颗粒的大集合体。在凝聚态物理和材料科学中，这些材料构成了一个挑战，因为它们的复杂行为超出了对普通固体或液体的既定预测。与此同时，颗粒材料的处理、储存和运输对我们的经济至关重要，而知识的提高为更好地控制提供了新的机会。这个项目的目标是建立一个基本的理解，即粒子碰撞如何推动凝聚成粒子团，以及静电在这一过程中扮演什么角色。这项研究以一种独特的实验设备为中心，在该设备中，自由落下的粒子流被成像并以非常高的空间和时间精度进行跟踪。更好地控制粒子聚集和电荷将影响从物理到工程再到环境科学的各个领域。带电粒子的聚集也与星际尘埃中聚集体的形成有关。该项目将培养一名博士生和一名博士后从事前沿材料研究，并包括本科生的积极参与。这项研究将与一系列多方面的教育和外联活动相结合，包括与附近的芝加哥科学与工业博物馆的活动。

****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.