Northwestern University

Mon 4:00 PM

Alexey Snezhko: Emergent Dynamics in Active Spinner Materials

When: Monday, February 26, 2018
4:00 PM - 5:00 PM  

Where: Technological Institute, M416, 2145 Sheridan Road, Evanston, IL 60208 map it

Audience: Faculty/Staff - Student - Public - Post Docs/Docs - Graduate Students

Contact: Beth Anne Siculan   847.491.3345

Group: McCormick-Engineering Sciences and Applied Mathematics

Category: Lectures & Meetings


Title: Emergent Dynamics in Active Spinner Materials

Speaker: Alex Snezhko, Material Science Division, Argonne National Laboratory

Abstract: Strongly interacting colloids driven out-of-equilibrium by an external periodic forcing often develop nontrivial collective dynamics. Active magnetic colloids proved to be excellent model experimental systems to explore emergent behavior and out-of-equilibrium phenomena. Ferromagnetic micro-particles, suspended at a liquid interface and energized by a uniaxial in-plane alternating magnetic field spontaneously form arrays of self-assembled spinners rotating in either direction. The spinners, emerging as a result of spontaneous symmetry breaking of clock/counterclockwise rotation of self-assembled particle chains generate vigorous vortical flows at the interface. An ensemble of spinners exhibits chaotic dynamics due to self-generated advection flows. Furthermore, erratic motion of spinners at the interface generates chaotic fluid flow reminiscent of two-dimensional turbulence. Rotational homogeneous alternating magnetic fields applied along the supporting interface, spontaneously form ensembles of synchronized self-assembled spinners. Experiments reveal nontrivial collective dynamics in large ensembles of synchronized magnetic spinners that can spontaneously form dynamic spinner lattices at the interface in a certain range of the excitation parameters. Magnetic micro-particles immersed in water and sediment on the bottom surface of the turn into colloidal rollers when energized by a single-axis homogeneous alternating magnetic field applied perpendicular to the surface supporting the particles. The rolling motion emerges as a result of spontaneous symmetry breaking of the particle rotations in external field in a certain range of excitation parameters. Experiments reveal a rich collective dynamics of magnetic rollers. Flocking and spontaneous formation of steady vortex motion have been observed. The effects are fine-tuned and
controlled by the parameters of the driving magnetic field.

The research was supported by the U.S. DOE, Office of Basic Energy Sciences, Division of Materials Science and Engineering.


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