Non-linear dielectric behaviour of 4,4′-n-hexylcyanobiphenyl near the nematic–isotropic phase transition

Abstract

The non-linear dielectric spectra of 4,4′-n-hexylcyanobiphenyl (6CB) were recorded in the frequency range 1–100 MHz in the presence of a strong static electric field E ₀ = 1 × 10⁷ V/m. The measurements were performed in the isotropic phase and the isotropic and nematic coexistence temperature region. Two absorption bands, related to intermolecular interactions (chemical bands), were observed in the non-linear dielectric relaxation spectra. The dynamic phenomena of the band which appears in the frequency region below 10 MHz in the vicinity of the phase transition between the isotropic and nematic phases were interpreted within the framework of the Landau–de Gennes theory for weakly first-order phase transitions. The second effect, with relaxation times 2–20 ns (about one order of magnitude lower, as in a process where the molecules are involved in pseudonematic domains), is expected to characterise the interaction processes of individual molecules.

Keywords:

• liquid crystals
• non-linear dielectric spectroscopy
• phase transitions
• intermolecular interactions

Acknowledgements

This work was supported by the Fonds voor Wetenschappelijk Onderzoek – Vlaanderen, Belgium, within the framework of an agreement for scientific cooperation with the Polish Academy of Sciences.