From adiabatic-scanning calorimetric results it is demonstrated that in mixtures of 9CB and 10CB, two compounds of the alkylcyanobiphenyl ($n\mathrm{CB}$) series, the nematic ($N$) to smectic-$A$ ($A$) transition becomes first order for narrow $N$ ranges. From the latent heats a tricritical point is located in the phase diagram. Measurements for 7CB+ 8CB mixtures show that the specific-heat exponent $\ensuremath{\alpha}$ depends on the width of the $N$ range for continuous $\mathrm{AN}$ transitions.

High-resolution X-ray data near the nematic (N)-smectic-A1 (SmA1) transition are reported for two polar liquid-crystal systems with large nematic ranges. The correlation volume ξ∥ ξ⊥2, the smectic order-parameter susceptibility σ, and the heat capacityCp of these systems and two other N-SmA1 systems are in excellent agreement with exact theoreticalpreasymptotic 3D-XY predictions. The importance of correction terms for ξ∥ ξ⊥2 and σ as well asCp is demonstrated. Universal features of the 3D-XY model are obeyed except for anisotropy in the correlation lengths ξ∥ and ξ⊥.

Nematic-Smectic- A Tricritical Point in Alkylcyanobiphenyl Liquid Crystals

Nonasymptotic critical 3D-XY behavior for the nematic-smectic-A1 liquid crystal transition

We report on the x-ray reflectivity of free-standing smectic films of 8CB. At temperatures well below the second-order nematic-to-smectic transition temperature TNA we find that the fluctuations of the smectic layers in the middle and at the surfaces have the same amplitude. However, on approaching TNA the fluctuations of the middle layers of the film are found to diverge while those at the surfaces are still quenched. The results can be understood qualitatively by including an additional surface term in the well-known Landau-De Gennes free energy for the smectic-A phase.

Nematic-Smectic- A Tricritical Point in Alkylcyanobiphenyl Liquid Crystals

Citations

Nonasymptotic critical 3D-XY behavior for the nematic-smectic-A1 liquid crystal transition

Critical Fluctuations in Free-Standing Smectic Films: An X-Ray Reflectivity Study

A density study

Phase Transitions in Rod‐Like Liquid Crystals

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