Supercolloidal Spinners: Complex Active Particles for Electrically Powered and Switchable Rotation

Abstract

A class of supercolloidal particles that controllably spin about their central axis in AC electric fields is reported. The rational design of these "microspinners" enables their rotation in a switchable manner, which gives rise to several interesting and programmable behaviors. It is shown that due to their complex shape and discrete metallic patches on their surfaces, these microspinners convert electrical energy into active motion via the interplay of four mechanisms at different electric field frequency ranges. These mechanisms of rotation include (in order of increasing frequency): electrohydrodynamic flows, reversed electrohydrodynamic flows, induced charge electrophoresis, and self-dielectrophoresis. As the primary mechanism powering their motion transitions from one phenomenon to the next, these microspinners display three directional spin inversions (i.e., from clockwise to anticlockwise, or vice versa). To understand the mechanisms involved, this experimental study is coupled with scaling analyses. Due to their frequency-switchable rotation, these microspinners have potential for applications such as interlocking gears in colloidal micromachines. Moreover, the principles used to power their switchable motion can be extended to design other types of supercolloidal particles that harvest electrical energy for motion via multiple electrokinetic mechanisms.

Hydrodynamics of random-organizing hyperuniform fluids

“…These differences demonstrate the robustness of fluidic HU, but also request a modified hydrodynamic theory for active spinner fluids to describe the 'odd viscosity' and topological waves in the fluids (46,47). Finally, we note that the suppressed density fluctuation was detected in a recent experimental air-driven spinner system (48) and we expect further experimental realization of hyperuniform spinner fluids using different techniques (49)(50)(51)(52)(53).…”

Active colloidal molecules assembled via selective and directional bonds

“…As we have shown, minor adjustment in AC frequency can have a profound impact on the assembly and dynamics of colloidal molecules. Apart from the influence of DEP, we can further understand this by superimposing the involved nonlinear electrokinetic mechanisms, EHD and ICEP, of two or multiple particles within an assembly, on the basis that both EHD and ICEP describe induced charges in diffusive layers that generate electroosmotic flows in response to the applied field 55,62 . For an assembly of colloidal molecule, the total flow U = U ICEP + U EHD , where U ICEP ∝ E 2 and U EHD ∝ E 2 f −1 .…”

Tadpole‐Shaped Catalytic Janus Microrotors Enabled by Facile and Controllable Growth of Silver Nanotails

“…Currently, there are two main types of microrotors. One is powered by external fields, such as magnetic fields, [ 16a,b,e,f,18 ] electric fields, [ 1c,19 ] and ultrasound, [ 8b,20 ] which apply torques to a colloidal particle and induces its rotation. Another type is chemically powered (often by catalytic reactions), where torque is introduced by either placing chemical reactions on only part of the particle, [ 21 ] or by designing an asymmetric shape.…”