“Now we want to expand the theory and apply it to more complicated systems. We want to demonstrate this theory for different classes of materials, and hopefully scientists and engineers in academia and industry can start using it to design and improve these systems.”Juan de Pablo, University of Chicago
The behavior of materials at the place where they connect and interact with other materials – the interface - is often a thorn in the side of scientists and engineers who want to understand and engineer systems that are well integrated and can seamlessly work with multiple components. In batteries, for example, the molecular processes that occur at the interfaces between the solid electrodes and the liquid electrolyte can limit the battery’s performance.
Using calculations and complex computer simulations, researchers from the University of Chicago’s Pritzker School of Molecular Engineering (PME) have developed a new theory for multicomponent interfaces that are far from equilibrium. This theory proves the long-held assumption of ‘local equilibrium’, the idea that though two substances might have vastly different temperatures or phases, their interface includes a small region where the system is in equilibrium. The researchers report their findings in the Proceedings of the National Academy of Sciences.
“Now we have a framework that anyone can use and apply to any type of material to better understand interfaces,” said Juan de Pablo, who led the research along with University of Chicago student Philip Rauscher and Hans Christian Oettinger from the ETH in Zürich, Switzerland.
De Pablo and his collaborators wanted to develop a theory that described exactly what happens at the interface of systems that are out of equilibrium. They chose to focus on systems involving two components and having two different phases with an interface between them.
Through calculations and computer simulations, the team took a model system – a mixture of a liquid and a gas at different temperatures – and developed a theory that describes what happens at their interface. This theory can describe, for example, a boiling liquid whose molecules escape into the adjacent vapor, which produces a complex dance at the interface.
“We’ve figured out a firmer basis for understanding molecular transport in systems with interfaces,” said Rauscher, a former postdoctoral researcher at the University of Chicago and co-author of the paper. “We now have a thermodynamically rigorous way to describe these systems.”
One key assumption proved by the new theory is that of local equilibrium – a concept from thermodynamics that states that even if the whole system is out of equilibrium, a small part of the interface will still be in equilibrium.
“To see local equilibrium at an interface that is out of equilibrium was better than we could have hoped for,” Rauscher said. “It had been an assumption, but now we have proven that it is true.”
Immediate applications for the theory include gas absorption and stripping, which is used to separate gas mixtures and remove impurities in industry, thereby reducing emissions and ultimately leading to less pollution.
“Now we want to expand the theory and apply it to more complicated systems,” de Pablo said. “We want to demonstrate this theory for different classes of materials, and hopefully scientists and engineers in academia and industry can start using it to design and improve these systems.”
This story is adapted from material from the University of Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.