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HomePhysicsSelf-Organized Zigzags from Fluid Stream

Self-Organized Zigzags from Fluid Stream

• Physics 16, 138

A zigzag association that seems spontaneously in a set of magnetic particles and another colloids is defined by the fluid circulation round every particle.

Magnetic particles in an oscillating magnetic subject type a zigzag sample. (Video is sped up by 8×.)

When molecules or micro organism set up right into a long-range sample, researchers wish to perceive how the microscopic interactions result in the macroscopic order. Pietro Tierno of the College of Barcelona and his colleagues noticed such self-organization in magnetic particles suspended in a liquid and subjected to an oscillating magnetic subject [1]. By means of experiments and simulations, the workforce confirmed that the ensuing zigzag sample is defined by the fluid circulation generated across the oscillating particles, not by any particulars of the particles or the utilized subject. Comparable zigzag patterns have additionally been seen in charged colloids subjected to oscillating electrical fields [2], so the reason could cowl a variety of particle programs. The researchers additionally consider that understanding and controlling the impact might result in helpful functions in microfluidics units.

Microscopic conveyor belt. The big-scale circulation sample is the sum of the flows round every particle.

The workforce’s 2.6-µm-long magnetic particles have been product of the iron oxide compound hematite. Every one had a peanut form, with two 1.2-µm-wide lobes separated by a narrower waist and a magnetic dipole second oriented perpendicular to its lengthy axis. The workforce positioned these particles in water combined with a little bit of polymer, which created a barely viscoelastic fluid, important for the sample formation. The particles sunk to a set depth the place gravity balanced electrostatic repulsion with the ground of the container, making the experiment totally two-dimensional. A sophisticated exterior magnetic-field oscillation induced every particle to roll like a pencil on a desk in alternate instructions about 4 occasions per second whereas maintaining its lengthy axis aligned with the others.

A simulation predicts the noticed patterns. The purple dots signify the magnetic particles, which circulation alongside the zigzag-shaped bands.

Tierno and his colleagues discovered that the rolling movement induced every particle to push fluid away on the ends of its two lobes (alongside the lengthy axis) and pull fluid in round its waist. Because of this, two close by particles would both entice or repel each other, relying on their relative positions. Nevertheless, the fluid-mediated pressure was minimized in 4 zones positioned round every particle at angles of +31° and –31° with respect to the lengthy axis. So the particles naturally migrated towards lengthy zigzagging bands inclined at these angles. However the particles weren’t frozen in these bands; as a substitute, the mixed fluid circulation from the person particles led to a conveyor-belt-type habits that moved the particles backwards and forwards alongside the bands. The researchers consider these long-distance flows may very well be used to ship chemical parts throughout a lab-on-a-chip machine.

–David Ehrenstein

David Ehrenstein is a Senior Editor for Physics Journal.


  1. G. Junot et al., “Massive scale zigzag sample rising from circulating energetic shakers,” Phys. Rev. Lett. 131, 068301 (2023).
  2. F. Katzmeier et al., “Emergence of colloidal patterns in ac electrical fields,” Phys. Rev. Lett. 128, 058002 (2022).

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