(43h) AC Field Powered Propulsion and Frequency-Controlled Steering of Engineered Metallo-Dielectric Microparticles

The transition from self-propelled particles to multifunctional motile microdevices requires the design of advanced active particles with complex shape, structure, and internally programmed responses. Our group has investigated a broad range of principles for assembly and propulsion of responsive and active colloidal structures driven by electric and magnetic fields. Here, we will specifically discuss how AC electric fields can endow engineered assymetric metallo-dielectric particles with directional propulsion energy and means of responding in complex ways to AC field parameters. The rich variety of mechanisms of motility in such systems include induced charge electrophoresis (Phys. Rev. Lett., 058302, 2008), electrohydrodynamic flows, reversed electrohydrodynamic flows and self-dielectrophoresis. The analysis of the origins, length-scales and time-scales of these mechanisms and their combined use and control by the frequency of the AC field enabled the design of new classes of microspinners and particles with complex engineered shapes that move on controllable trajectories. These particles can change direction of motility, and can also be steered and reversibly assembled by the AC field. We will present examples of particles that include: (1) Supercolloidal microspinners that display up to three frequency-dependent switching of direction of rotation (Adv. Funct. Mater. 1803465, 2018); (2) “Star Trek” microswimmers that can move multi-directionally and can reversibly assemble in trains; (3) Asymmetric microcubes and shaped particles that can controllably switch between individual multi-directional active motility and massively assembled states.