Reconfigurable structure and tunable transport in synchronized active spinner materials

Abstract

Ensembles of actuated colloids are excellent model systems to explore emergent out-of-equilibrium structures, complex collective dynamics, and design rules for the next generation materials. Here, we demonstrate that ferromagnetic microparticles suspended at an air-water interface and energized by an external rotating magnetic field spontaneously form dynamic ensembles of synchronized spinners in a certain range of the excitation field parameters. Each spinner generates strong hydrodynamic flows, and collective interactions of the multiple spinners promote a formation of dynamic lattices. On the basis of experiments and simulations, we reveal structural transitions from liquid to nearly crystalline states in this novel active spinner material and demonstrate that dynamic spinner lattices are reconfigurable, capable of self-healing behavior and that the transport of embedded inert cargo particles can be remotely tuned by the parameters of the external excitation field. Our findings provide insights into the behavior of active spinner materials with reconfigurable structural order and tunable functionalities.

Reconfigurable emergent patterns in active chiral fluids

“…Active spinner fluids, comprised of autonomous spinning units, enable unique dynamic phases and transport characteristics [27][28][29][30][31] . A significant effort, both experimental and theoretical, has been recently dedicated to understanding of fundamental rules governing the emergence of collective states in active colloids comprised of spinning units 28,[32][33][34][35][36][37][38][39] .…”

Ultrasound Doppler-guided real-time navigation of a magnetic microswarm for active endovascular delivery

“…2E . In region I, relatively long nanoparticle chains were formed and tended to repel each other because of the strong hydrodynamic repulsion ( 28 , 29 ). By adjusting the field parameters ( d ms and frequency of magnetic field f ), chains were fragmented into shorter chains, and a dynamic-equilibrium microswarm was formed (∼800 μm in radius, region II).…”

Transport and Assembly of Magnetic Surface Rotors**

“…Recently developed approaches exploiting dynamic self‐assembly of magnetic colloidal particles provide a robust method for generating large ensembles of microscopic spinners [46–48] . It has been demonstrated that the application of a uniaxial external magnetic field oscillating in‐plane of the interface supporting ferromagnetic spherical particles can lead to multiple self‐assembled spinners with a narrow size distribution, see Figure 8.…”

“…Transport characteristics of such spinner liquids are not trivial. The active diffusion (diffusive motion of passive particles promoted by the activity of the spinner sub‐system) increases linearly with the spinner density and is approximately independent of the frequency of the driving field [48] . Moreover, it was demonstrated that the dependence of the active diffusion coefficient on the inert particle size is non‐monotonic.…”