Clustering and Charging in Granular Flows

****技术摘要****该项目采用粒状材料的自由落体流，在两个紧密耦合的研究努力中研究粒子的相互作用和聚集。首先，对同材料颗粒的摩擦荷电现象进行了研究，这是一种具有重要科学意义和应用价值的现象，其具体机制仍在争论中。在稀粒状流中，当颗粒进入均匀电场区域时，跟踪带摩擦电荷的颗粒，可以收集颗粒电荷的完整统计分布及其与晶粒尺寸的依赖关系。这项工作的结果不仅可以更好地理解产生摩擦充电的基本机制，还可以帮助控制摩擦充电。其次，通过增加流内的粒子密度，可以系统地增加粒子-粒子相互作用的概率。这使得诱导粒子捕获过程成为可能，并在现场跟踪随后的聚集成更大的团簇，首次详细研究了短程内聚力和远程静电力的相互作用。该项目将培养1名前沿材料研究领域的博士研究生和1名博士后，并包括本科生的积极参与。该项目的研究部分将与多方面的教育和推广活动相结合，包括与附近的芝加哥科学与工业博物馆的活动。****非技术摘要****颗粒材料是小颗粒的大集合体。在凝聚态物理和材料科学中，这些材料提出了一个挑战，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颗粒材料开辟了新的机会。这个项目的目标是建立一个基本的理解粒子碰撞如何驱动团聚成粒子簇，以及静电充电在这个过程中起什么作用。这项研究围绕着一个独特的实验设施进行，在这个实验设施中，自由落体的粒子流被成像并以非常高的空间和时间精度跟踪。更好地控制粒子聚集和充电将影响物理、工程和环境科学等领域。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1名前沿材料研究领域的博士研究生和1名博士后，并包括本科生的积极参与。这项研究将与多方面的教育和推广活动相结合，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.