Rounding of Phase Transitions in Cylindrical Pores

TL;DR

This paper investigates how phase transitions in cylindrical pores are smoothed out due to finite size effects, using models and simulations to reveal the transition sequence and differences between finite and infinite pores.

Contribution

It provides a detailed analysis of phase transition rounding in cylindrical pores, highlighting the sequence of transitions and differences between finite and infinite geometries.

Findings

Finite pores exhibit a two-step transition process.

A first rounded transition from coexistence to multi-domain state.

A second transition to homogeneous phase near pore criticality.

Abstract

Phase transitions of systems confined in long cylindrical pores (capillary condensation, wetting, crystallization, etc.) are intrinsically not sharply defined but rounded. The finite size of the cross section causes destruction of long range order along the pore axis by spontaneous nucleation of domain walls. This rounding is analyzed for two models (Ising/lattice gas and Asakura-Oosawa model for colloid-polymer mixtures) by Monte Carlo simulations and interpreted by a phenomenological theory. We show that characteristic differences between the behavior of pores of finite length and infinitely long pores occur. In pores of finite length a rounded transition occurs first, from phase coexistence between two states towards a multi-domain configuration. A second transition to the axially homogeneous phase follows near pore criticality.