Effect of Chain Flexibility on Nematic-Smectic Transition

TL;DR

This paper presents a theoretical analysis showing that chain flexibility induces a strong first-order nematic-smectic transition, contrasting with the weak transition seen in rigid rods, and aligns with recent experimental data.

Contribution

It introduces a density-functional and tube-model approach to demonstrate the impact of chain flexibility on phase transition nature.

Findings

Flexibility causes a strong first-order transition.

Calculated spinodal volume fraction matches experiments.

Period of modulation instability aligns with observed data.

Abstract

The theory of nematic-smectic phase transition in the system of uniform semi-flexible chains with hard-core repulsion is presented. Both the general density-functional formalism the tube-model calculation show that the flexibility of the chains results in a strong first-order transition, in contrast to the common weak-cristallization scenario of the nematic-smectic transition in rigid rods. The calculated spinodal volume fraction of the uniform nematic phase and the period of the modulation instability are consistent with recent experimental results.