Self-organized composites of multiwalled carbon nanotubes and nematic liquid crystal 5CB: Optical singularities and percolation behavior in electrical conductivity

TL;DR

This study explores how multi-walled carbon nanotubes and nematic liquid crystal composites exhibit optical singularities and electrical percolation, revealing network formation and phase transition effects relevant for optoelectronic applications.

Contribution

It demonstrates the self-organization, network formation, and optical singularities in MWCNT-LC composites near the percolation threshold, highlighting their complex interactions.

Findings

Formation of micron-sized MWCNT aggregates with fractal boundaries.

Spanning MWCNT networks form near 0.025% wt, causing conductivity transition.

Optical singularities arise from laser interaction with LC shells around MWCNTs.

Abstract

This work discusses optical singularities and electrical conductivity behavior in a thin electrooptical cell filled with composites including multi-walled carbon nanotubes (MWCNTs) and nematic liquid crystal (LC). The MWCNTs with high aspect ratio $L/d\approx 300\div1000$ and nematic LC 5CB (4-pentyl-4-0-cyanobiphenyl) were used. The composites were prepared by introduction of MWCNTs ($0.0001\div0.1$ % wt) into LC solvent with subsequent sonication. The increase of MWCNT concentration (between $0.005\div0.05$ % wt) resulted in self-organization of MWCNTs and formation of micron-sized aggregates with fractal boundaries. The visually observed formation of spanning MWCNT networks near the percolation threshold at ~0.025 % wt was accompanied with transition from non-conductive to conductive state and generation of optical singularities. The observed effects were explained by the strong interactions between MWCNTs and LC medium and planar orientation of 5CB molecules near the lateral surface of MWCNTs. It was speculated that optical singularities arose as a results of interaction of an incident laser beam with LC perturbed interfacial shells covering the MWCNT clusters. Behavior of the interfacial shell thickness in external electric field and in the vicinity of the nematic to isotropic transition was discussed.