Although most natural and synthetic¹ processes prefer to settle into equilibrium²（均衡，平静） -- 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 fluctuations³, freezing and melting, or movement. These conditions allow humans to regulate their body temperature, airplanes to fly, and Earth to rumble⁴ with seismic⁵ 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'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 the McCormick School of Engineering and Applied⁶ 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（振荡的） potentials," which was featured in the June 23 issue of the Proceedings⁷ of the National Academy of Sciences.

 

Past research has shown that theoretical, non-equilibrium particle structures can self-organize when continuously injected with energy, 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."

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