Dielectric properties of selected laterally fluoro-substituted 4,4′′-dialkyl, dialkoxy and alkyl-alkoxy [1:1′;4′:1′′]terphenyls

Abstract

Measurements of the complex permittivity, ε* = ε′ – iε″, within the frequency range 200 Hz to 10 MHz for 15 laterally fluoro-substituted terphenyls have been conducted. In most cases the substances exhibited the nematic phase over a broad temperature range. All substances were characterised by negative dielectric anisotropy, and are potentially useful for vertical alignment mode systems. The static permittivity tensor components have been analysed in relation to the dipole structure of the molecules. Dielectric relaxation processes observed in the liquid crystalline (LC) and solid rotator (R) phases (obtained by slow cooling of the samples) are characterised by calculation of the relaxation times and activation barriers. The rotation motions around the short axes are typical for LC phases, whereas rotations about the long axes, accompanied in some cases by internal motions, are present in the R phase.

Keywords:

• liquid crystal
• nematic
• negative dielectric anisotropy
• dielectric properties
• terphenyl

Acknowledgements

This work was partially supported by the executive programme of scientific and technological co-operation between the Italian Republic and Poland 2007–2009 (Project No. 8), and was financed in part by the EU under contract number IST–028154 and by Polish grant PBS 765. Joanna Czub is thanked for her help in carrying out the measurements.