Forming Zigzags

An illustration showing the flow field formed around magnetic particles (orange) in a viscoelastic fluid. The areas of attraction (blue) and repulsion (yellow) create a zig-zag pattern between particles.

Scientists are fascinated by the organized patterns that can emerge from non-living systems. Here, researchers study micron-sized magnetic particles, immersed in a viscoelastic fluid and subjected to an oscillating magnetic field. The peanut-shaped particles roll around their long axis and assemble to form millimeter-sized bands of zigzags. These patterns, the researchers found, do not depend on the particles’ specific shape or on the details of the applied magnetic field. Instead, the zigzags depend only on the symmetry of the flow generated around each particle. In their system, illustrated above, each particle pushed fluid away along their long axis and drew in fluid toward their waist; as a result, particle pairs would attract or repel, depending on their relative orientation. That interparticle force ultimately caused the particles to self-organize into zigzags. (Image, video, and research credit: G. Junot et al.; via APS Physics)

This sped-up animation shows the zig-zag pattern that the particles self-organization into.
This sped-up animation shows the zigzag pattern that the particles self-organization into.
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