Elasticity of Confined Simple Fluids from an Extended Peng-Robinson Equation of State

Thermodynamic properties of fluids in nanopores are alteredbyconfinement, and equations of state (EOS) for bulk fluids are notable to predict them. We utilized a recent EOS based on the Peng-RobinsonEOS, which takes into account the effects of confinement, to derivean analytical expression for the elastic properties of the fluid,isothermal bulk modulus, or compressibility. We calculated the modulusof liquid argon confined in model spherical nanopores of various sizes.We compared the predictions based on the EOS to calculations of thebulk modulus directly from Monte Carlo simulations in the grand canonicalensemble (GCMC). The bulk modulus of argon in mesopores predictedby the EOS appeared consistent with the GCMC predictions, showingin particular linear dependence on Laplace pressure and on the inversepore size. Furthermore, the EOS appeared capable of predicting themodulus of the fluid in micropores, where GCMC predictions failed.Our result is a step toward developing an equation of state for confinedfluids, which can be used for predictions of elasticity.

Automated summary

We derived an analytical expression for the elastic properties of a fluid confined in nanopores based on an equation of state (EOS) that considers the effects of confinement. The predictions of the EOS for the bulk modulus of liquid argon in nanopores were consistent with Monte Carlo simulations, showing linear dependence on Laplace pressure and the inverse pore size. Furthermore, the EOS was capable of predicting the modulus of the fluid in micropores, where Monte Carlo simulations failed. Our research is a step towards developing an equation of state for confined fluids that can be used for predictions of elasticity.