An Analytic Model for Nano Confined Fluids Phase-Transition (Applications for Confined Fluids in Nanotube and Nanoslit)

TL;DR

This paper introduces an analytic model that predicts phase transitions in nano-confined fluids, accounting for wall effects and tensorial pressure, applicable to nanotubes and nanoslits, and demonstrates size-dependent critical temperature behavior.

Contribution

The model uniquely incorporates wall effects and tensorial pressure to predict phase transitions in nano systems, extending classical thermodynamics to nanoscale confinement.

Findings

Predicts liquid-vapor phase transition and critical point in nano systems.

Shows critical temperature increases with system size, approaching macroscopic values.

Demonstrates local density and phase fragmentation during transitions.

Abstract

In this report, an analytic model to predict phase transitions of confined fluids in nano systems is presented and it is used to predict the behavior of the confined fluid in nanotubes and nanoslits. In our approach besides including a third degree of freedom due to wall effect to define the state of the system, the tensorial character for pressure is considered. Using the perturbation theory of statistical mechanics it is shown that the van der Waals equation of state is equally valid for small as well as large systems. The model proposed is shown to predict the liquid-vapor phase transition as well as the critical point in any size confined fluid systems. It is also shown that the critical temperature increases with the size of the nano system and finally it reaches the macroscopic critical temperature value as the diameter of the nanotube (or width of the nanoslit) approaches infinity. The proposed model can also demonstrate the existence of the local density and phase fragmentations during phase transitions in a confined nano system.