Bulk inhomogeneous phases of anisotropic particles: A fundamental measure functional study of the restricted orientations model

TL;DR

This study uses a fundamental measure functional approach to analyze the phase behavior of anisotropic particles with restricted orientations, revealing complex inhomogeneous phases including a novel discotic smectic phase.

Contribution

It introduces a detailed FMF-based analysis of the restricted orientations model, uncovering new stable phases and comparing them with simulation results.

Findings

Identification of a rich phase diagram with multiple inhomogeneous phases.

Discovery of a stable discotic smectic phase unique to the restricted orientations model.

Qualitative agreement with existing simulation data on anisotropic particles.

Abstract

The phase diagram of prolate and oblate particles in the restricted orientations approximation (Zwanzig model) is calculated. Transitions to different inhomogeneous phases (smectic, columnar, oriented, or plastic solid) are studied through minimization of the fundamental measure functional (FMF) of hard parallelepipeds. The study of parallel hard cubes (PHC's) as a particular case is also included motivated by recent simulations of this system. As a result a rich phase behavior is obtained which include, apart from the usual liquid crystal phases, a very peculiar phase (called here discotic smectic) which was already found in the only existing simulation of the model, and which turns out to be stable because of the restrictions imposed on the orientations. The phase diagram is compared at a qualitative level with simulation results of other anisotropic particle systems.