Ultrasonically Levitated Granular Matter

非技术摘要：更好地了解颗粒物质，一类由大量粒子碰撞和聚集而成的材料，对于广泛的工业过程和自然现象都很重要，包括星际尘埃形成行星的最初阶段。该项目引入了一个新的实验平台，其中小颗粒被声学悬浮，它们的排列可以在计算机控制下操纵，它们的相互作用可以精确测量。对颗粒之间这种相互作用的详细研究解决了物理学和材料科学中的许多基本问题，并且关于聚集体形成的知识的改进为更好地控制涉及细颗粒处理的工业过程提供了新的机会。该项目培训一名研究生，一名博士后学者和几名本科生，向他们介绍材料研究的前沿问题，并让他们参与科学推广活动。技术摘要：该项目的重点是亚毫米级颗粒，这些颗粒很容易带电，因此表现出短程接触力和长程静电力的丰富相互作用。为了精确地测量这些力，同时提供一种用于受控颗粒操纵的手段，超声波悬浮产生一种稳定的环境，在这种环境中，重力通过声压平衡，从而可以观察到微小的颗粒-颗粒相互作用。一个特殊的方面是在计算机控制下可以在真实的时间内改变的声压场的实现。这使得以前不可能的实验成为可能，例如在重复的粒子-粒子碰撞期间测量电荷转移。合适的声学势也可以产生相同电荷极性的粒子晶格，类似于尘埃等离子体中的库仑晶体。重要的是，宏观粒子的集合很容易被驱动到强相互作用的状态，其中相互作用势远远超过环境热能。该项目的两个重点是开发可编程的多粒子捕获和操纵声腔，并研究由大量悬浮粒子组成的系统的集体行为。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Abstract:The better understanding of granular matter, a class of materials comprised of large numbers of particles that collide and aggregate, is important for a wide range of industrial processes as well as natural phenomena, including the very beginning of planet formation from interstellar dust. The project introduces a new experimental platform, in which small particles are levitated acoustically, their arrangement can be manipulated under computer control, and their interactions can be measured with precision. The detailed investigation of such interactions among particles addresses many fundamental problems in physics and materials science, and improved knowledge about aggregate formation opens new opportunities for better control of industrial processes that involve the handling of fine particles. The project trains one graduate student, one postdoctoral scholar, and several undergraduate students, introduces them to forefront issues in materials research, and involves them in science outreach activities. Technical Abstract:The project focuses on sub-millimeter scale particles, which can easily become charged and as a result exhibit a rich interplay of short-range contact forces and longer-ranged electrostatic forces. To measure these forces with precision while providing a means for controlled particle manipulation, ultrasonic levitation generates a stable environment in which gravity is balanced by acoustic pressure so that minute particle-particle interactions become observable. A special aspect is the implementation of a sound pressure field that can be changed in real time under computer control. This enables experiments that previously have not been possible, such as the measurement of charge transfer during repeated particle-particle collisions. Suitable acoustic potentials also can produce lattices of particles of the same charge polarity, similar to Coulomb crystals in dusty plasmas. Importantly, ensembles of macroscopic particles are easily driven into the strongly interacting regime, where the interaction potential far exceeds the ambient thermal energy. Two thrusts of the project develop a programmable acoustic cavity for multi-particle trapping and manipulation, and investigate the collective behavior of systems comprised of large numbers of levitated particles.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.