# Disclosing the True Critical Point of Fluids Confined in Nanopores

## TL;DR

This paper compares two methods to determine the critical point of fluids in nanopores and identifies which one gives the true critical point.

## Contribution

The study is the first to compare two methods on the same system to determine the true critical point of confined fluids.

## Key findings

- The DSC method identifies the true critical point where no heat is released.
- The Peng–Robinson equation of state accurately models the capillary-condensation curve using the true PCP.

## Abstract

Two methods for determining the pore critical point (PCP),
i.e.,
the critical point of confined fluid, are currently available in the
literature. The better-known method is based on the analysis of data
obtained from adsorption isotherms, while the newer method analyzes
the heat of capillary condensation data obtained from differential
scanning calorimetry (DSC). For the first time, these two methods
are implemented on the same confined system for comparison to explore
which method provides the true PCP. While the heat released at the
PCP derived from adsorption isotherms is measurably nonzero, implying
that a phase transition still occurs in the pores, no heat is released
at the PCP derived from the DSC measurements, which indicates the
true critical point of the first-order phase transition. With this
true PCP, the Peng–Robinson cubic equation of state (EOS),
without any modification, is shown to accurately represent the whole
capillary-condensation curve of confined pure fluids with small and
large molecules as well as a confined mixture.