Impact of homeotropic and planar alignment of liquid crystalline medium on the structure and dielectric properties of modified fullerene mC₆₀+ E25M mixtures

Abstract

The microstructure and dielectric properties of nematic liquid crystals (LCs) E25M (cyanobiphenyls/terphenyl mixture) doped by modified fullerene mC₆₀ (with weight concentration C within 0–3 wt%) were investigated at different temperatures (298–343 K). The fullerene C₆₀ was modified by 1,8-octanediamine in order to improve its affinity to LC media. Sandwich-type 25 μm thick glass cells with planar (┴) and homeotropic (||) alignments of LC media inside them were used. The optical microscopic data evidenced the presence of more homogeneous spatial distribution of aggregates for || alignment in comparison to that observed for || alignment. The dielectric studies revealed different dielectric properties (activation energies W, relaxation times τ and bulk electrical conductivities σ _B ) of pure E25M and mC₆₀+E25M mixtures in dependence of medium alignment. Different inequalities W _|| < W _┴ in pure Е25М and W _┴ < W _|| in mC₆₀+Е25М mixtures were observed for the near-electrode layers and the bulk electrical conductivity components. This evidenced the presence of different charge transfer mechanisms, depending on alignment of the LC medium.

Keywords:

• liquid crystal
• fullerene C60
• planar and homeotropic alignment
• optical microscopy
• dielectric properties
• percolation threshold
• aggregation

Acknowledgements

This work was supported in part by Projects 1.4.1. В/134 and 2.16.1.4. The authors also thank Dr E.V. Basiuk (Golovataya-Dzhymbeeva), Universidad Nacional Autónoma de México, for providing the sample of modified fullerene C₆₀, Dr O.P. Boiko for the help with measurements of micro-photos and Dr N.S. Pivovarova for her help with preparation of the manuscript.