The role of string-like, supramolecular assemblies in reentrant supernematic liquid crystals

TL;DR

This study uses simulations to explore how string-like supramolecular assemblies in reentrant nematic liquid crystals enhance molecular mobility, revealing a confinement-induced packing effect that leads to high diffusivity along the director.

Contribution

It demonstrates the formation of supramolecular, string-like conformations in reentrant nematic phases and links these structures to enhanced self-diffusion in confined liquid crystals.

Findings

Reentrant nematic phase exhibits high nematic order and increased diffusivity.

Supramolecular strings form due to confinement-induced packing effects.

String-like assemblies facilitate parallel movement of molecules as trains.

Abstract

Using a combination of isothermal-isobaric Monte Carlo and microcanonical molecular dynamics we investigate the relation between structure and self-diffusion in various phases of a model liquid crystal using the Gay-Berne-Kihara potential. These molecules are confined to a mesoscopic slit-pore with atomically smooth substrate surfaces. As reported recently [see M. G. Mazza {\em et al.}, Phys. Rev. Lett. {\bf 105}, 227802 (2010)], a reentrant nematic (RN) phase may form at sufficiently high pressures/densities. This phase is characterized by a high degree of nematic order and a substantially enhanced self-diffusivity in the direction of the director $\hat{\bm{n}}$ which exceeds that of the lower-density nematic and an intermittent smectic A phase by about an order of magnitude. Here we demonstrate that the unique transport behavior in the RN phase may be linked to a confinement-induced packing effect which causes the formation of supramolecular, string-like conformations. The strings consist of several individual molecules that are capable of travelling in the direction of $\hat{\bm{n}}$ as individual "trains" consisting of chains of molecular "cars". Individual trains run in parallel and may pass each other at sufficiently high pressures.