Nav: Home

Sound waves direct particles to self-assemble, self-heal

June 19, 2017

An elegantly simple experiment with floating particles self-assembling in response to sound waves has provided a new framework for studying how seemingly lifelike behaviors emerge in response to external forces.

Scientists at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) demonstrated how particles, floating on top of a glycerin-water solution, synchronize in response to acoustic waves blasted from a computer speaker.

The study, published today (Monday, June 19) in the journal Nature Materials, could help address fundamental questions about energy dissipation and how it allows living and nonliving 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," said Xiang Zhang, corresponding author of the paper and a senior faculty scientist at Berkeley Lab's Materials Sciences Division with a joint appointment at UC Berkeley. "However, the underlying principles governing this are only partially understood. This work provides a simple yet elegant platform to study and understand such phenomena."

To hear some physicists describe it, this state of non-equilibrium, characterized by the ability to constantly change and evolve, is the essence of life. It applies to biological systems, from cells to ecosystems, as well as to certain nonbiological systems, such as weather or climate patterns. Studying non-equilibrium systems gets theorists a bit closer to understanding how life -- particularly intelligent life -- emerges.

However, it is complicated and hard to study because non-equilibrium systems are open systems, Zhang said. He noted that physicists like to study things that are stable and in closed systems.

"We show that individually 'dumb' particles can self-organize far from equilibrium by dissipating energy and emerge with a collective trait that is dynamically adaptive to and reflective of their environment," said study co-lead author Chad Ropp, a postdoctoral researcher in Zhang's group. "In this case, the particles followed the 'beat' of a sound wave generated from a computer speaker."

Notably, after the researchers intentionally broke up the particle party, the pieces would reassemble, showing a capacity to self-heal.

Ropp noted that this work could eventually lead to a wide variety of "smart" applications, such as adaptive camouflage that responds to sound and light waves, or blank-slate materials whose properties are written on demand by externally controlled drives.

While previous studies have shown that particles are capable of self-assembly in response to an external force, this paper presents a general framework that researchers can use to study the mechanisms of adaptation in non-equilibrium systems.

"The distinction in our work is that we can predict what happens - how the particles will behave - which is unexpected," said another co-lead author Nicolas Bachelard, who is also a postdoctoral researcher in Zhang's group.

As the sound waves traveled at a frequency of 4 kilohertz, the scattering particles moved along at about 1 centimeter per minute. Within 10 minutes, the collective pattern of the particles emerged, where the distance between the particles was surprisingly non-uniform. The researchers found that the self-assembled particles exhibited a phononic bandgap - a frequency range in which acoustic waves cannot pass - whose edge was inextricably linked, or "enslaved," to the 4 kHz input.

"This is a characteristic that was not present with the individual particles," said Bachelard. "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 experimental design could hardly have been simpler. For the waveguide, the researchers used a 2-meter-long acrylic tube that contained a 5-millimeter-deep pool of a glycerin-water solution. The particles were made from straws floating on top of a flat piece of plastic, and the sound source came from off-the-shelf computer speakers that researchers directed into the tube via a plastic funnel. Measuring the sound waves proved to be the most technical part of the experiment.

"This is something you could do yourself in your garage," said Ropp. "It was a dirt-cheap experiment with parts that are available at your corner hardware store. At one point, we needed bigger straws, so I went out and bought some boba tea. The setup was extremely simple, but it showed the physics beautifully."

The experiment focused on acoustic waves because soundproofing was easier to achieve, but the principles underlying the behavior they observed would be applicable to any wave system, the researchers said.

This fundamental research could form the basis for developing intelligent networks that perform simple non-algorithmic computation, with a future toward systems that perform sentient-like decision making, the researchers said.

"I can think of parallels to artificial brains, with sections that respond to different frequency 'brain waves' that are malleable and reconfigurable," said Ropp.
This work was supported by the Office of Naval Research and DOE's Office of Science.

Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel Prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit

DOE's Office of Science is the single largest supporter of basic research in

DOE/Lawrence Berkeley National Laboratory

Related Physics Articles:

Challenges and opportunities for women in physics
Women in the United States hold fewer than 25% of bachelor's degrees, 20% of doctoral degrees and 19% of faculty positions in physics.
Indeterminist physics for an open world
Classical physics is characterized by the equations describing the world.
Leptons help in tracking new physics
Electrons with 'colleagues' -- other leptons - are one of many products of collisions observed in the LHCb experiment at the Large Hadron Collider.
Has physics ever been deterministic?
Researchers from the Austrian Academy of Sciences, the University of Vienna and the University of Geneva, have proposed a new interpretation of classical physics without real numbers.
Twisted physics
A new study in the journal Nature shows that superconductivity in bilayer graphene can be turned on or off with a small voltage change, increasing its usefulness for electronic devices.
Physics vs. asthma
A research team from the MIPT Center for Molecular Mechanisms of Aging and Age-Related Diseases has collaborated with colleagues from the U.S., Canada, France, and Germany to determine the spatial structure of the CysLT1 receptor.
2D topological physics from shaking a 1D wire
Published in Physical Review X, this new study propose a realistic scheme to observe a 'cold-atomic quantum Hall effect.'
Helping physics teachers who don't know physics
A shortage of high school physics teachers has led to teachers with little-to-no training taking over physics classrooms, reports show.
Physics at the edge
In 2005, condensed matter physicists Charles Kane and Eugene Mele considered the fate of graphene at low temperatures.
Using physics to print living tissue
3D printers can be used to make a variety of useful objects by building up a shape, layer by layer.
More Physics News and Physics Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 3: Shared Immunity
More than a million people have caught Covid-19, and tens of thousands have died. But thousands more have survived and recovered. A week or so ago (aka, what feels like ten years in corona time) producer Molly Webster learned that many of those survivors possess a kind of superpower: antibodies trained to fight the virus. Not only that, they might be able to pass this power on to the people who are sick with corona, and still in the fight. Today we have the story of an experimental treatment that's popping up all over the country: convalescent plasma transfusion, a century-old procedure that some say may become one of our best weapons against this devastating, new disease.   If you have recovered from Covid-19 and want to donate plasma, national and local donation registries are gearing up to collect blood.  To sign up with the American Red Cross, a national organization that works in local communities, head here.  To find out more about the The National COVID-19 Convalescent Plasma Project, which we spoke about in our episode, including information on clinical trials or plasma donation projects in your community, go here.  And if you are in the greater New York City area, and want to donate convalescent plasma, head over to the New York Blood Center to sign up. Or, register with specific NYC hospitals here.   If you are sick with Covid-19, and are interested in participating in a clinical trial, or are looking for a plasma donor match, check in with your local hospital, university, or blood center for more; you can also find more information on trials at The National COVID-19 Convalescent Plasma Project. And lastly, Tatiana Prowell's tweet that tipped us off is here. This episode was reported by Molly Webster and produced by Pat Walters. Special thanks to Drs. Evan Bloch and Tim Byun, as well as the Albert Einstein College of Medicine.  Support Radiolab today at