New approach to form non-equilibrium structures

July 24, 2014

Although most natural and synthetic processes prefer to settle into equilibrium—a state of unchanging balance without potential or energy—it is within the realm of non-equilibrium conditions where new possibilities lie. Non-equilibrium systems experience constant changes in energy and phases, such as temperature fluctuations, freezing and melting, or movement. These conditions allow humans to regulate their body temperature, airplanes to fly, and the Earth to rumble with seismic activity.

But even though these conditions exist naturally and are required for the most basic life, they are rarely understood and difficult to find in synthetic materials.

"In equilibrium thermodynamics, we know everything," said Northwestern University's Igal Szleifer. "Non-equilibrium thermodynamics is an old subject, but we don't have a complete set of rules for it. There are no guidelines."

Szleifer is the Christina Enroth-Cugell Professor of Biomedical Engineering and professor of chemical and biological engineering in Northwestern's McCormick School of Engineering and Applied Science, professor of chemistry in the Weinberg College of Arts and Science, and professor of medicine at the Feinberg School of Medicine.

Szleifer, his postdoctoral fellow Mario Tagliazucchi, and Emily Weiss, the Irving M. Klotz Research Professor of Chemistry at Weinberg, have developed a new technique for creating non-equilibrium systems, which will bring scientists closer to understanding the fundamentals of the mysterious topic. Their work is described in the paper "Dissipative self-assembly of particles interacting through time-oscillatory potentials," which was featured in the June 23 issue of the Proceedings of the National Academy of Sciences.

Past research has shown that theoretical, non-equilibrium particle structures can self-organize when continuously injected with , but strategies for injecting energy were limited.

"Think about us as humans," Szleifer said. "For us to be alive, we need to use energy all the time. In order to do that, we have to be out of equilibrium. We are trying to understand non-equilibrium assembly systems, so we have to give them energy."

Using models and simulations, Tagliazucchi, Weiss, and Szleifer found that they could give equilibrium systems energy by using a mixture of pH-responsive particles. Varying pH levels flipped the electric charges of the particles, causing them to oscillate and create the energy needed to assemble into non-equilibrium structures.

"By controlling the structure of the material, we can control its properties as well," Szleifer said. "The moment you stop the oscillations, the structure disappears."

The oscillatory method has allowed Szleifer and his collaborators to create novel structures that are impossible to find in conditions. He said scientists could potentially determine how they want particles to interact and then tailor oscillations to lead to that outcome.

"For a number of years, my group has tried to find rules for self assembly," Szleifer said. "This is building toward that. We want to make guidelines for experimentalists."

Explore further: Slow road to stability for emulsions

Related Stories

Slow road to stability for emulsions

December 9, 2011

By studying the behavior of tiny particles at an interface between oil and water, researchers at Harvard have discovered that stabilized emulsions may take longer to reach equilibrium than previously thought.

Non-equilibrium quantum states in atmospheric chemistry

September 3, 2012

(Phys.org)—Research that sheds new light on the microscopic chemical physics driving one of the most important reaction sequences in atmospheric chemistry is published in Science today by Dr David Glowacki from the University ...

Force is the key to granular state-shifting

February 15, 2013

Ever wonder why sand can both run through an hourglass like a liquid and be solid enough to support buildings? It's because granular materials – like sand or dirt – can change their behavior, or state. Researchers from ...

Technique simplifies the creation of high-tech crystals

July 22, 2014

Highly purified crystals that split light with uncanny precision are key parts of high-powered lenses, specialized optics and, potentially, computers that manipulate light instead of electricity. But producing these crystals ...

Recommended for you

Light-powered 3-D printer creates terahertz lens

April 29, 2016

From visible light to radio waves, most people are familiar with the different sections of the electromagnetic spectrum. But one wavelength is often forgotten, little understood, and, until recently, rarely studied. It's ...

A tiny switch for a few particles of light

April 29, 2016

The Jedi knights of the Star Wars saga are engaged in an impossible fight. This does not result from the superiority of the enemy empire, but from physics because laser swords cannot be used for fighting like metallic blades: ...

Physicists detect the enigmatic spin momentum of light

April 25, 2016

Ever since Kepler's observation in the 17th century that sunlight is one of the reasons that the tails of comets to always face away from the sun, it has been understood that light exerts pressure in the direction it propagates. ...

Superfast light source made from artificial atom

April 26, 2016

All light sources work by absorbing energy – for example, from an electric current – and emit energy as light. But the energy can also be lost as heat and it is therefore important that the light sources emit the light ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

ViperSRT3g
not rated yet Jul 28, 2014
This sounds akin to self-organization when shaking a bucket full of legos. With enough shaking (energy input) there is the slight chance that the legos will slowly self-organize and align themselves so that they are all stacked up nice and neatly. The same analogy could be applied to containers full of other regularly shaped items like a box of nails or matches.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.