Polymeric nematics of associating rods: phase behavior, chiral propagation and elasticity

TL;DR

This paper develops a second-virial theory for associating rod-like colloids, exploring their phase behavior, elasticity, and the effects of tip interactions, including polymerization and chirality, on nematic liquid crystal phases.

Contribution

It introduces a model that captures the transition from monomeric to polymeric nematic phases in rod colloids, incorporating flexibility, chirality, and tip interactions.

Findings

Stable nematic phases can form without polymerization at high temperatures.

Tip potential changes enable a crossover from monomeric to polymeric nematic fluids.

Polymerization inhibitors narrow the biphasic region and induce reentrant nematization.

Abstract

Rod-shaped colloids with attractive tips can form linear aggregates that may subsequently undergo hierarchical self-assembly into nematic fluids. Inspired by recent modelling efforts on chromonic liquid crystals, composed of discotic building blocks, we formulate a second-virial theory for reversible supramolecular rods. Unlike chromonics, these systems are capable of forming stable nematic phases in the high-temperature, monomeric limit in the absence of polymerization. Changing the tip potential from attractive to repulsive thus enables a smooth crossover from a monomeric to a polymeric nematic fluid. We analyze the isotropic-nematic phase behavior for both regimes and address the nematic elastic properties. The theory accounts for the molecular flexibility and chirality of the filaments and respects the intrinsic chain-length dependence of nematic order. We also discuss the impact of polymerization inhibitors on the phase behavior in the polymeric regime and find that the inhibitors cause a marked narrowing of the isotropic-nematic biphasic region, and generate reentrance nematization as well as a mass density inversion of the coexisting phases. We finally discuss the elastic moduli of rod-based polymeric nematics by qualitative comparing their elastic anisotropies with those of chromonic liquid crystals and other nanoparticle-based nematics.