NSF-BSF: From microscopic propulsion to macroscale dynamics: Active particle transport in complex environments

自推进微粒悬浮液，或“微游泳者”，无论是生物的还是合成的，在过去的十年里，从生物物理学到材料科学再到工程学，在各种各样的学科中引起了相当大的兴趣。从生物学的角度来看，了解微游泳者的运动策略与繁殖、疾病传播和环境污染过程有关。在工程上，活性微粒被设计用于小尺度运输材料和驱动齿轮和其他装置。然而，由于对其推进策略、与环境的相互作用以及宏观尺度传输特性的不完全理解，限制了微游泳者在实际应用中的广泛使用。该项目是加州大学圣地亚哥分校和以色列理工学院的合作项目，将使用数学建模和数值模拟来加强对复杂环境和几何形状中活跃粒子输运的基本理解，以及微尺度推进与宏观尺度输运和流体动力学之间的关系。该项目还将通过吸引研究生和本科生参与研究，将研究纳入加州大学圣地亚哥分校和以色列理工学院的课程，以及为高中生开设夏季流体力学入门课程，来支持教育和推广活动。该项目将运用数学建模和高保真数值模拟相结合的方法来解决与推进机制、有效传输和微型游泳者及其悬架的大规模动力学相关的突出问题。该项目将研究自扩散胶体的推进模式，并通过阐明溶质对流和弛豫、粒子形状以及与刚性或软边界的相互作用的影响，改进现有的自扩散电泳推进模型。该团队还将利用宏观输运理论和平均场模型开发微游泳者输运的统计模型，以研究稀和半稀系统中自走式游泳者在通道和周期性多孔介质中的长期输运特性。最后，该项目将通过开发电泳游泳者的统计描述来连接其主题，以解决电泳机制和传输统计相耦合的问题。该奖项反映了美国国家科学基金会的法定使命，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。

Suspensions of self-propelled microparticles, or "microswimmers," whether biological or synthetic, have generated considerable interest over the last decade in a wide variety of disciplines, from biophysics to materials science to engineering. From a biological standpoint, understanding locomotion strategies of microswimmers is relevant to reproduction, the spread of disease and contamination processes in the environment. In engineering, active microparticles have been designed to transport material on small scales and to actuate gears and other devices. Nevertheless, the widespread use of microswimmers in practical applications is limited by an incomplete understanding of their propulsion strategies, interactions with their environment, and macroscale transport properties. This project, which is a collaboration between University of California - San Diego and the Technion, will use mathematical modeling and numerical simulations to enhance fundamental understanding of active particle transport in complex environments and geometries and the relationships between microscale propulsion and macroscale transport and hydrodynamics. This project will also support educational and outreach activities by engaging graduate and undergraduate students in the research, by incorporating the research in courses at UCSD and the Technion, and by presenting a summer introductory course on fluid mechanics for high-school students.This project will apply a combination of mathematical modeling and high-fidelity numerical simulations to address outstanding problems related to propulsion mechanisms, effective transport, and large-scale dynamics of microswimmers and their suspensions. The project will examine propulsion modalities of autophoretic colloids and will improve on existing models of self-diffusiophoretic propulsion by elucidating the effects of solute convection and relaxation, particle shape and interactions with rigid or soft boundaries. The team will also develop statistical models of microswimmer transport by using macrotransport theory and mean-field modeling to investigate long-time transport properties of self-propelled swimmers in channels as well as periodic porous media in both dilute and semi-dilute systems. Finally, the project will connect its themes by developing statistical descriptions of phoretic swimmers for problems where the phoretic mechanism and statistics of transport are coupled.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.