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

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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.