Positional ordering of hard adsorbate particles in tubular nanopores

TL;DR

This study investigates the structural phase behavior of hard particles confined in narrow cylindrical nanopores, revealing a transition from fluid-like to ordered states and highlighting discrepancies with classical theories.

Contribution

It reformulates the transfer operator method to analyze monolayer structures in cylindrical pores, providing new insights into phase transitions and ordering in confined hard particle systems.

Findings

No true phase transition occurs in the examined pore sizes.

Hard spheres transition from fluid-like to zigzag solid order with increasing density.

Hard cylinders exhibit continuous layering between one-row and two-row monolayers.

Abstract

The phase behaviour and structural properties of a monolayer of hard particles is examined in such a confinement, where the adsorbed particles are constrained to the surface of a narrow hard cylindrical pore. The diameter of the pore is chosen such that only first and second neighbour interactions occur between the hard particles. The transfer operator method of Percus and Zhang [Mol. Phys., 69, 347 (1990)] is reformulated to obtain information about the structure of the monolayer. We have found that a true phase transition is not possible in the examined range of pore diameters. The monolayer of hard spheres undergoes a structural change from fluid-like order to a zigzag-like solid one with increasing surface density. The case of hard cylinders is different in the sense that a layering takes place continuously between a low density one-row and a high density two-row monolayer. Our results reveal a clear discrepancy with classical density functional theories, which do not distinguish smectic-like ordering in bulk from that in narrow periodic pores.