Fluids confined in nanosized pores do not thermodynamically behave the same way as fluids in macrosized volumes because interactions between the fluid and the wall become important. Understanding these systems would help advance many applications that utilize nanoporous media, like perovskite solar cells, lithium-ion batteries, and carbon-dioxide capture. Bråten et al. developed a thermodynamic framework that successfully predicts the properties of liquids and gases in nanoconfined systems.
The team’s framework, called the Nano-Equation of State, or Nano-EoS, predicts the thermodynamic properties of nanoconfined, pure liquids and gases with a wide range of geometries, sizes, interparticle interactions, and wall-particle interactions —which previous methods could not consistently describe.
“We present a consistent thermodynamic framework that represents an equation of state for pure, confined fluids,” co-author Øivind Wilhelmsen said. “By comparing it to results from molecular simulations of fluids in spherical pores of different sizes, where the fluid interacts with the pore wall, we show that the Nano-EoS reproduces values for the internal energy and the pressure nearly within the accuracy of the simulations.”
The authors developed their equation of state by using a combination of terms. A bulk equation describes the fluid not touching the wall, while Gibbs’ framework accounts for excess properties and enables a theoretical description of the surface contribution for fluids touching the wall. Molecular simulations allowed the researchers to extract relevant numerical quantities. To verify their framework, they compared the predicted results with numerical simulations.
Wilhelmsen said there is much more work to be done, such as describing systems under extreme confinement.
Source: “Equation of state for confined fluids,” by Vilde Bråten, Daniel Tianhou Zhang, Morten Hammer, Ailo Aasen, Sondre Kvalvåg Schnell, and Øivind Wilhelmsen, Journal of Chemical Physics (2022). The article can be accessed at https://doi.org/10.1063/5.0096875.
This paper is part of the 2022 JCP Emerging Investigators Special Collection, learn more here.