Static and dynamic dielectric effects in the vicinity of the isotropic to nematic phase transition in 7CB

Abstract

Static and dynamic dielectric measurements were performed with very high accuracy on a mesogenic compound n‐heptylcyanobiphenyl (7CB) in the isotropic (I) and nematic (N) phases. The critical‐like temperature behaviour of the static permittivity of isotropic 7CB in the vicinity of the I–N phase transition can be described with the critical exponent close to 0.5, indicating the tricritical nature of the transition. Anomalously slow rotational diffusion (subdiffusion), characterized by a fractal value of the diffusion exponent α, is observed in the vicinity of the I–N transition with a lambda‐like profile of the exponent temperature dependence.

Acknowledgments

This work was partially supported by the Center of Excellence for Magnetic and Molecular Materials for Future Electronics within European Commission Contract No. G5Ma‐CT‐2002‐04049; by the Fonds voor Wetenschappelijk Onderzoek‐Vlaanderen, Belgium, in the framework of the agreement for scientific cooperation with the Polish Academy of Sciences; and by the Polish Committee for Scientific Research (KBN) in the framework of Project No 2P 03B 078 25.