National Science Foundation-funded scientists used sound waves to levitate particles, revealing new insights about how materials cluster together in the absence of gravity -- principles which underlie everything from how molecules assemble to the very early stages of planet formation from space dust. Much of the universe is made up of particles assembling. With acoustic levitation, the researchers have a model system to study assembly at scales visible to the human eye, where we can track each particle with precision, and then relate the results to a wide range of often much more microscopic phenomena. The team was interested in the shape of prototypical clusters that form when, starting from a single particle, more are added one by one. They used sound waves to levitate plastic particles in midair -- each about one millimeter in diameter, about the thickness of a penny -- and studied how these particles interact with each other as they formed clusters, broke up and then reassembled into different configurations. The research team now intends to look at how acoustic levitation can bring together larger numbers of particles to assemble more complex structures.
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