Mesophase formation in a system of top-shaped hard molecules: Density functional theory and Monte Carlo simulation

TL;DR

This study combines density functional theory and Monte Carlo simulations to analyze phase behavior of top-shaped molecules, revealing how the central sphere influences phase stability and transitions.

Contribution

It introduces a combined theoretical and simulation approach to understand phase stability in top-shaped molecules with a central sphere.

Findings

Central sphere destabilizes nematic and smectic A phases.

Increasing cylinder length stabilizes nematic phase.

Large central spheres favor smectic C over smectic A.

Abstract

We present the phase diagram of a system of mesogenic top-shaped molecules based on the Parsons- Lee density functional theory and Monte Carlo simulation. The molecules are modeled as a hard spherocylinder with a hard sphere embedded in its center. The stability of five different phases is studied, namely, isotropic, nematic, smectic A, smectic C, and columnar phases. The positionally ordered phases are investigated only for the case of parallel alignment. It is found that the central spherical unit destabilizes the nematic with respect to the isotropic phase, while increasing the length of the cylinder has the opposite effect. Also, the central hard sphere has a strong destabilizing effect on the smectic A phase, due the inefficient packing of the molecules into layers. For large hard sphere units the smectic A phase is completely replaced by a smectic C structure. The columnar phase is first stabilized with increasing diameter of the central unit, but for very large hard sphere units it becomes less stable again. The density functional results are in good agreement with the simulations.