Polydispersity stabilizes Biaxial Nematic Liquid Crystals

TL;DR

This study demonstrates that size polydispersity in boardlike particles enhances the stability and range of biaxial nematic liquid crystal phases, revealing new phase diagram features.

Contribution

It introduces a theoretical analysis showing how polydispersity induces a novel phase topology with increased biaxial stability in liquid crystals.

Findings

Polydispersity creates two Landau tetracritical points in the phase diagram.

A large stable biaxiality regime appears between uniaxial nematic and smectic phases.

Polydispersity favors oblate over prolate uniaxial nematic order.

Abstract

Inspired by the observations of a remarkably stable biaxial nematic phase [E.v.d. Pol et al., Phys. Rev. Lett. 103, 258301 (2009)], we investigate the effect of size polydispersity on the phase behavior of a suspension of boardlike particles. By means of Onsager theory within the restricted orientation (Zwanzig) model we show that polydispersity induces a novel topology in the phase diagram, with two Landau tetracritical points in between which oblate uniaxial nematic order is favored over the expected prolate order. Additionally, this phenomenon causes the opening of a huge stable biaxiality regime in between uniaxial nematic and smectic states.