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Legendre-Fenchel transforms capture layering transitions in porous media

Abstract

We have investigated the state of a nanoconfined fluid in a slit pore in the canonical and isobaric ensembles. The systems were simulated with molecular dynamics simulations. The fluid has a transition to a close-packed structure when the height of the slit approaches the particle diameter. The Helmholtz energy is a non-convex function of the slit height if the number of particles does not exceed that of one monolayer. As a consequence, the Legendre transform cannot be applied to obtain the Gibbs energy. The Gibbs energy of a non-deformable slit pore can be transformed into the Helmholtz energy of a deformable slit pore using the Legendre-Fenchel transform. The Legendre-Fenchel transform corresponds to the Maxwell construction of equal areas.
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Category

Academic article

Language

English

Author(s)

  • Olav Galteland
  • Eivind Bering
  • Kim Kristiansen
  • Dick Bedeaux
  • Signe Kjelstrup

Year

2022

Published in

Nanoscale Advances

Volume

4

Issue

12

Page(s)

2660 - 2670

View this publication at Norwegian Research Information Repository