Phase behaviour of hard cylinders

TL;DR

This study maps the phase diagram of hard cylindrical particles using advanced Monte Carlo simulations, revealing various stable and metastable phases for both prolate and oblate shapes, with implications for biological systems.

Contribution

It provides a comprehensive phase diagram for hard cylinders, including new insights into stable and metastable phases, using an improved overlap detection algorithm.

Findings

Identification of stable isotropic, nematic, smectic, and crystal phases for prolate cylinders.

Discovery of stable cubatic, nematic, and columnar phases for oblate cylinders.

Clarification of metastable phases and triple point coexistences in the phase diagrams.

Abstract

Using isobaric Monte Carlo simulations, we map out the entire phase diagram of a system of hard cylindrical particles of length $L$ and diameter $D$, using an improved algorithm to identify the overlap condition between two cylinders. Both the prolate $L/D>1$ and the oblate $L/D<1$ phase diagrams are reported with no solution of continuity. In the prolate $L/D>1$ case, we find intermediate nematic \textrm{N} and smectic \textrm{SmA} phases in addition to a low density isotropic \textrm{I} and a high density crystal \textrm{X} phase, with \textrm{I-N-SmA} and \textrm{I-SmA-X} triple points. An apparent columnar phase \textrm{C} is shown to be metastable as in the case of spherocylinders. In the oblate $L/D<1$ case, we find stable intermediate cubatic \textrm{Cub}, nematic \textrm{N}, and columnar \textrm{C} phases with \textrm{I-N-Cub}, \textrm{N-Cub-C}, and \textrm{I-Cub-C} triple points. Comparison with previous numerical and analytical studies is discussed. The present study, accounting for the explicit cylindrical shape, paves the way to more sophisticated models with important biological applications, such as viruses and nucleosomes.