Nematic-nematic demixing in polydisperse thermotropic liquid crystals

TL;DR

This paper investigates how polydispersity influences phase separation in thermotropic liquid crystals, revealing that increased polydispersity can cause multiple nematic phases and re-entrant phase behavior, with implications for understanding complex liquid crystal systems.

Contribution

It demonstrates that polydispersity induces nematic-nematic phase separation and re-entrant behavior in thermotropic liquid crystals using a Maier-Saupe theoretical framework.

Findings

Polydispersity causes phase separation into multiple nematic phases.

Increased polydispersity widens the isotropic-nematic coexistence region.

Re-entrant isotropic-nematic phase separation occurs at high polydispersity.

Abstract

We consider the effects of polydispersity on isotropic-nematic phase equilibria in thermotropic liquid crystals, using a Maier-Saupe theory with factorized interactions. A sufficient spread (approx. 50%) in the interaction strengths of the particles leads to phase separation into two or more nematic phases, which can in addition coexist with an isotropic phase. The isotropic-nematic coexistence region widens dramatically as polydispersity is increased, leading to re-entrant isotropic-nematic phase separation in some regions of the phase diagram. We show that similar phenomena will occur also for non-factorized interactions as long as the interaction strength between any two particle species is lower than the mean of the intra-species interactions.