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

摘要

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