Tunable self-healing of magnetically propelling colloidal carpets

Abstract

The process of crystallization is difficult to observe for transported, out-of-equilibrium systems, as the continuous energy injection increases activity and competes with ordering. In emerging fields such as microfluidics and active matter, the formation of long-range order is often frustrated by the presence of hydrodynamics. Here we show that a population of colloidal rollers assembled by magnetic fields into large-scale propelling carpets can form perfect crystalline materials upon suitable balance between magnetism and hydrodynamics. We demonstrate a field-tunable annealing protocol based on a controlled colloidal flow above the carpet that enables complete crystallization after a few seconds of propulsion. The structural transition from a disordered to a crystalline carpet phase is captured via spatial and temporal correlation functions. Our findings unveil a novel pathway to magnetically anneal clusters of propelling particles, bridging driven systems with crystallization and freezing in material science.

Reconfigurable emergent patterns in active chiral fluids

“…Both systems demonstrate a remarkable level of complex collective behavior ranging from emergence of flocks to formation of global vortices controlled by activity 38 , 40 , 42 . However, aside from systems with prescribed direction of motility 36 , 43 our understanding of the role shape anisotropy plays in the emergence of a collective motion and self-assembly in active spinner fluids remains unexplored. In this letter, we employ shape-anisotropic Quincke rollers to introduce active chiral rollers and reveal a plethora of novel collective dynamic patterns emerging away from equilibrium.…”

Swarming Microdroplets to a Dexterous Micromanipulator

“…When the ellipticity reaches 0 and the pitch angle is 30°, the FSM begins to curl and rolls up into an RSM after 35 s. In addition to the counterclockwise bending from top to bottom, the bending direction of the FSMs can be controlled (Figure S2 and Movie S4, Supporting Information). Compared to previous solid‐like microswarms, [ 41–43 ] the proposed FSM in this work exhibits more degrees of freedom and morphological flexibility. The fission behavior of the microswarm can also be realized by regulating the external magnetic field (Figure S3, Supporting Information).…”

Programmed magnetic manipulation of vesicles into spatially coded prototissue architectures arrays

“…As a versatile, noninvasive, and cost-effective strategy, magnetic manipulation has been increasingly exploited for the scalable assembly of magnetic and nonmagnetic objects into twodimensional (2D) or three-dimensional (3D) metastructures based on their responses to inhomogeneous magnetic field in two mechanisms: positive magnetophoresis (moving to areas with maximized field intensity) for magnetic objects 14,15 , and negative magnetophoresis (moving to areas with minimized field intensity) for objects with lower magnetic susceptibility than that of suspension media 16,17 . Compared with the well-established study and wide application of the first mechanism, the investigation of the second mechanism is still in its infancy, but attracts intense attentions in recent years because of its universal applicability for different kinds of inanimate and living materials 18,19 , and unique manipulation behaviors for the objects going beyond Earnshaw's theorem 20 .…”