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.
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