Phase behavior of wormlike rods

TL;DR

This study uses Molecular Dynamics simulations to explore how internal flexibility in rodlike particles affects their phase behavior, notably destabilizing the smectic A phase while leaving other phase transition characteristics unchanged.

Contribution

It provides new insights into the destabilization of the smectic A phase due to particle flexibility, confirmed through detailed simulation analysis.

Findings

Smectic A phase is destabilized by increased particle flexibility.

Nematic--to--smectic A transition remains first order regardless of flexibility.

No evidence found for a columnar phase in flexible rods.

Abstract

By employing Molecular Dynamics computer simulations, the phase behavior of systems of rodlike particles with varying degree of internal flexibility has been traced from the perfectly rigid rod limit till very flexible particles, and from the high density region till the isotropic phase. From the perfectly rigid rod limit and enhancing the internal flexibility, the range of the smectic A phase is squeezed out by the concomitant action of the scarcely affected crystalline phase at higher density and the nematic phase at lower density, until it disappears. These results confirm the supposition, drawn from previous theoretical, simulational and experimental studies, that the smectic A phase is destabilized by introducing and enhancing the degree of particle internal flexibility. However, no significant changes in the order of nematic--to--smectic A phase transition, which appears always first order, nor in the value of the layer spacing, are observed upon varying the degree of particle internal flexibility. Moreover, no evidence of a columnar phase, which was tought of as a possible superseder of the smectic A phase in flexible rods, has been obtained.