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Sound waves can now be used to direct floating particles to self-assemble and self-heal.

Scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have discovered that particles floating on top of a glycerin-water solution can synchronize in response to acoustic waves blasted from a computer speaker.

The study could be used to address fundamental questions regarding energy dissipation and how it allows living and non-living systems to adapt to their environment when they are out of thermodynamic equilibrium.

“Dynamic self-assembly under non-equilibrium is not only important in physics, but also in our living world,” Xiang Zhang, corresponding author of the paper and a senior faculty scientist at Berkeley Lab’s Materials Sciences Division, said in a statement. However, the underlying principles governing this are only partially understood. “This work provides a simple yet elegant platform to study and understand such phenomena.”

The researchers intentionally broke up the particles and saw that the pieces can reassemble and have the capacity to self-heal.

This could eventually lead to smart applications including adaptive camouflage that responds to sound and light waves or blank-slate materials whose properties are written on demand by externally controlled devices. The research can also serve as the basis for developing intelligent networks that perform simple non-algorithmic computation, with a future toward systems that perform sentient-like decision making.

As the sound waves traveled at a four kilohertz frequency, the scattering particles moved along at about one centimeter per minute. Within 10 minutes, the collective pattern of the particles emerged, where the distance between the particles was non-uniform and the self-assembled particles exhibited a photonic bandgap—a frequency range where acoustic waves cannot pass—whose edge was inextricably linked to the 4 kHz input.

“This is a characteristic that was not present with the individual particles,” co-lead author Nicolas Bachelard, a postdoctoral researcher in Zhang’s group, said in a statement. “It only appeared when the particles collectively organized, which is why we call this an emergent property of our structure under non-equilibrium conditions.”

The researchers used a two-meter long acrylic tube that contained a five millimeter deep pool of a glycerin-water solution to create the waveguide. They created the particles from straws floating on top of a flat piece of plastic.
 

 

 

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