Static and dynamic critical behaviours in de Vries liquid crystals

Abstract

Measurements of dielectric dispersion have been carried out on two liquid crystal compounds 8422[2F3] and 8O23[7F8-], showing non-layer-shrinkage (NLS) behaviour through the smectic-A (Sm-A)–smectic-C (Sm-C) transition. The critical exponent γ for the susceptibility determined from the data lies in the range 1.9–2.0 for 8422[2F3] and 1.1–1.2 for 8O23[7F8-]. While the former agrees with the general trend reported so far for this group of liquid crystals, the latter result is distinct from them, the γ value being definitely smaller. These observations indicate that the Sm-A–Sm-C transition with NLS behaviour can exhibit quasi two-dimensional Ising critical behaviour under certain conditions. The critical exponent Δ for the relaxation frequency has also been obtained as Δ = 2.0–2.1 for 8422[2F3] and 1.2–1.3 for 8O23[7F8-]. The results support the general expectation Δ > γ rather than the conventional behaviour Δ = γ.

Keywords:

• critical phenomena
• dielectric dispersion
• relaxation frequency
• de Vries liquid crystals

Acknowledgements

The authors are grateful to Professor C.C. Huang and Professor H. Takezoe for helpful discussions, and Professor Y. Takanishi for technical help in the dielectric measurements. The liquid-crystal compounds were kindly provided by 3M Company, St Paul, Minnesota, USA. This work has been supported in part by the Global Center of Excellence Program by MEXT, Japan, through the Nanoscience and Quantum Physics Project of the Tokyo Institute of Technology.