Simulating surface tension in a non-equilibrium system

For decades, physicists have studied surface tension in equilibrium systems. But in reality there are many physical systems, such as bacterial colonies, that operate far from equilibrium. The lack of a comprehensive understanding of and the paucity of existing models for the surface tension of systems away from equilibrium has prevented scientists from developing a deep understanding of the properties of fluctuating non-equilibrium assemblies. A new paper by del Junco and Vaikuntanathan uses simulations to explore the physics of surface tension in a simple, prototype non-equilibrium system.

“We are interested in surface tension, because energy along the surface has a lot to do with how particles self-assemble,” said Clara del Junco, who is a graduate student in Vaikuntanathan’s lab. They discovered that in some circumstances they could ‘tweak’ the surface tension of the non-equilibrium system by changing certain properties of the material and predict the response n a surprisingly simple and universal manner.

“We wanted to take a very small step and go out of equilibrium but still control material properties,” said Vaikuntanathan, an assistant professor in chemistry at the University of Chicago. “We found a reasonably simple way to control surface tension by changing certain properties that exert forces on the material.”

This work offers the opportunity to explore new ways to manipulate materials and how they respond to the surroundings.

“It was exciting to see that you can tune one external control parameter and get a linear increase in the surface tension in response,” said del Junco. “We don’t really understand why we get this one-to-one relation between the magnitude of the control parameter and the surface tension. We will need to study it further in future work.”

Source: “Interface height fluctuations and surface tension of driven liquids with time-dependent dynamics,” by Clara del Junco and Suriyanarayanan Vaikuntanathan, The Journal of Chemical Physics (2019). The article can be accessed at https://doi.org/10.1063/1.5042251 .