Directed propulsion of spherical particles along three dimensional helical trajectories

Abstract

Active colloids are a class of microparticles that ‘swim’ through fluids by breaking the symmetry of the force distribution on their surfaces. Our ability to direct these particles along complex trajectories in three-dimensional (3D) space requires strategies to encode the desired forces and torques at the single particle level. Here, we show that spherical colloids with metal patches of low symmetry self-propel along non-linear 3D trajectories when powered remotely by an alternating current (AC) electric field. In particular, particles with triangular patches of approximate mirror symmetry trace helical paths along the axis of the field. We demonstrate that the speed and shape of the particle’s trajectory can be tuned by the applied field strength and the patch geometry. We show that helical motion can enhance particle transport through porous materials with implications for the design of microrobots that can navigate complex environments.

Cargo capture and transport by colloidal swarms

“…1A): (i) sensing the system state via particle tracking, i.e., the self-propelled particle positions and orientations and cargo position; (ii) calculating self-propulsion speeds of each particle based on the current state and desired future state (based on a control objective); and (iii) actuating each particle's speed by considering light-activated self-propelled colloids on a light array [e.g., a liquid-crystal display (35) screen surface]. Actuation could also be achieved on spatially addressable electrodes or other arrays that mediate locally actuated transport mechanisms (36)(37)(38)(39), which could modify some terms of the dynamic model, but the control problem would be conceptually similar.…”

Catalytically propelled 3D printed colloidal microswimmers

“…One such study showed that L-shaped particles exhibit circular trajectories. 22 More recent experiments on select anisotropic shapes or patches confirmed some of the predictions in 2D [23][24][25][26] and found unexpected motion patterns such as non-cylindrical helices 27 in 3D. Still, the current limitations in particle design prevent a systematic comparison with theory.…”

Recent Advances in Motion Control of Micro/Nanomotors

“…More recently, Lee et al [81] developed special spherical colloids with metal patches ( Figure 5A). When remotely powered by an AC electric field, these designed particles exhibited a predefined 3D helical movement along the axis of the field with a controllable speed and shape of trajectory turned by the applied field strength and patch geometry.…”

“…Reproduced with permission. [81] Copyright 2019, Springer Nature. B) Schematic diagram of an interdigitated microelectrodes system where, upon the application of AC electric fields, metallodielectric Janus particles are hydrodynamically confined and electrokinetically propelled in one dimension along the electrode center lines with tunable speeds.…”