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Under magnet's sway, fluids form simple structures

Droplets wiggle, split and coalesce into simple and dynamic configurations

SELF-ASSEMBLING  SCULPTURE  A dollop of ferrofluid under  the influence of a magnetic field can split and arrange itself into simple  droplets (left) and complex, warping formations (right).

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Dollops of magnetic fluid can assemble themselves into both simple structures and constantly changing complex formations, researchers report in the July 19 Science.

In nature, molecules such as proteins can autonomously warp and fold themselves into new arrangements. Scientists want to create self-assembling synthetic structures that are as dynamic and versatile as the natural ones that drive life.

Physicist Jaakko Timonen at Aalto University in Finland and colleagues figured they could do that with ferrofluids, liquids that contain suspended magnetic nanoparticles and behave in strange ways when exposed to magnetic fields. The researchers placed a droplet of ferrofluid atop a nonstick surface and gradually moved a magnet toward the surface from below. The strengthening magnetic field caused the droplet to split into simple, evenly spaced daughter droplets.

Then Timonen and his team oscillated the magnet horizontally, moving it increasingly faster and over longer distances. At certain thresholds of speed and distance, the droplets suddenly coalesced into elongated globules that changed shape as the magnet yanked them back and forth.

Timonen says the demonstration should help scientists better understand and exploit dynamic self-assembly.

A rapidly oscillating magnet causes ferrofluid droplets to coalesce into elongated, dynamic structures.
Credit: Courtesy of Science/AAAS

A dollop of ferrofluid divides into daughter droplets (and several very small pellets) when exposed to a magnetic field.
Credit: Courtesy of Science/AAAS

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