Collaborative Research: Active Colloids under AC Electric Fields: From Single Particle Motion to Collective Dynamics

微观物体的主动运输对于维持生物物种的生物活性是必不可少的。虽然自然界已经进化到拥有复杂的生化马达，但合成马达的发展还远远落后。近年来，研制出了一种新型的交流电场驱动合成电机，有望实现智能微机械的按需控制。然而，目前的电动力学理论并不能一致地解释它们在不同电场条件下的推进行为。将进行一项补充性的实验和计算研究，以模拟马达周围的流体动力学流动，从而揭示控制单个马达和大型马达整体运动的潜在物理机制。这项研究将提供必要的基础知识，为技术的发展，以操纵微观和纳米尺度的对象与空间和时间的规则。教育和拓展活动，如开发K-12公立学校的学习模块和本科生的研究暑期体验项目，也将以鼓励代表性不足的群体参与大学科学和工程项目为目标。该项目的目标是了解不对称粒子的电流体动力学如何影响它们的主动行为，从单粒子运动到小簇形成再到紧急集体动力学。具体的研究任务包括三个方面：(1)阐明介电粒子在低频和高频下的电流体动力推进机制；(2)揭示了小团簇组装过程中流体动力相互作用、空间效应、布朗运动和静电相互作用之间复杂的相互作用；(3)研究数千个直线电机和旋转纺丝机的集体行为。通过在粒子中创造不对称特性和调整不同的场条件，实验框架将允许系统地研究不对称粒子的推进，并揭示低频和高频下潜在的不同推进机制，从而显著推进电动力学领域。在研究感兴趣的长度和时间尺度时，具有可调分辨率的计算方法也将能够在精度和成本之间取得平衡。实验和数值模拟之间的详细比较将提供重要的见解，并有助于揭示电液动力马达的潜在物理特性。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。

The active transport of microscopic objects is essential for maintaining the bioactivities of living species. Although nature has evolved to possess complex biochemical motors, the development of synthetic motors lags far behind. Recently, a new type of synthetic motor driven by an alternating current electric field was developed, which hold promise for on-demand control of intelligent micro-machines. However, current electrokinetic theory cannot consistently explain their propulsion behavior under different field conditions. A complementary experimental and computational study will be performed to model the hydrodynamic flow surrounding the motors and thus reveal the underlying physical mechanisms that govern the motion of both individual and a large ensemble of motors. This research will provide the fundamental knowledge necessary for the development of technologies to manipulate micro- and nano-scale objects with both spatial and temporal regulations. Education and outreach activities, such as the development of learning modules for K-12 public schools and research summer experience programs for undergraduates, will also be developed with the goal to encourage the participation of underrepresented groups toward university science and engineering programs. The goal of this project is to understand how the electrohydrodynamics of asymmetric particles influence their active behavior ranging from single particle motion to small cluster formation to emergent collective dynamics. Three specific research tasks will be performed: (1) Elucidate the electrohydrodynamic propulsion mechanisms of dielectric particles at both low and high frequencies; (2) Reveal the intricate interplay between hydrodynamic interaction, steric effects, Brownian motion, and electrostatic interaction in the assembly of small clusters; and (3) Investigate the collective behavior of thousands of linear motors and rotating spinners. The experimental framework, by creating asymmetric properties in particles and tuning different field conditions, will allow systematic studies of the propulsion of asymmetric particles and reveal potentially different propulsion mechanisms at low and high frequencies, thus significantly advancing the field of electrokinetics. The computational methods with tunable resolution will also be able to achieve a balance between accuracy and cost, as required for studying the length and time scale of interest. A detailed comparison between experiments and numerical modeling will provide crucial insights and help reveal the underlying physics of electrohydrodynamic motors.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.