Prenematic Fluctuations in Nanoparticle-Hosted Systems

TL;DR

This paper combines experiments and simulations to explore how nanoparticles influence pretransitional phenomena in liquid crystals, revealing universal behavior and defect-induced microscopic mechanisms affecting dielectric properties.

Contribution

It provides a microscopic explanation for pretransitional effects in nanoparticle-doped liquid crystals, bridging the gap between macroscopic observations and molecular dynamics.

Findings

NPs do not alter the isotropic-nematic transition temperature

Pretransitional effects show universal critical behavior

Nanoparticles act as seeds for topological defects, affecting dielectric response

Abstract

This study combines broadband dielectric spectroscopy (BDS) experiments with molecular dynamics (MD) simulations to investigate the influence of nanoparticle (NP) inclusions on pretransitional phenomena in a liquid crystal (LC) host. We aimed to fill the existing gap between macroscopic observations and their microscopic origins. Our experimental results on SiO$_2$-doped 5CB composites demonstrate that while NP additions do not significantly change the isotropic-nematic transition temperature ($T_c$), the pretransitional effects exhibit universal behavior, confirmed by identical critical exponents across all samples. The observed systematic decrease in dielectric permittivity is explained by MD simulations, which reveal that nanoparticles act as "seeds" for topological defects, forcing the surrounding LC molecules into a "hedgehog" configuration. This static, defect-induced structure leads to a local antiparallel alignment and cancellation of molecular dipoles, providing a direct microscopic mechanism for the macroscopic dielectric response and successfully bridging the micro-macro scales.