Phase Behavior and Characterization of Heptamethyltrisiloxane-based De Vries Smectic Liquid Crystal by Electro-optics, X Rays, and Dielectric Spectroscopy
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Electrical and electronic engineering
A heptamethyltrisiloxane liquid crystal (LC) exhibiting I–SmA ∗–SmC ∗ phases has been characterized by calorimetry, polarizing microscopy, x-ray diffraction, electro-optics, and dielectric spectroscopy. Observations of a large electroclinic effect, a large increase in the birefringence with electric field, a low shrinkage in the layer thickness (∼1.75%) at 20 °C below the SmA ∗–SmC ∗ transition, and low values of the reduction factor (∼0.40) suggest that the SmA ∗ phase in this material is of the de Vries type. The reduction factor is a measure of the layer shrinkage in the SmC ∗ phase and it should be zero for an ideal de Vries. Moreover, a decrease in the magnitude of an with decreasing temperature indicates the presence of the temperature-dependent tilt angle in the SmA ∗ phase. The electro-optic behavior is explained by the generalized Langevin-Debye model as given by Shen et al. [Y. Shen et al., Phys. Rev. E 88, 062504 (2013)]. The soft-mode dielectric relaxation strength shows a critical behavior when the system goes from the SmA ∗ to the SmC ∗ phase.
Sreenilayam, S.P. et al (2017). Phase behavior and characterization of heptamethyltrisiloxane-based de Vries smectic liquid crystal by electro-optics, X rays, and dielectric spectroscopy. Physical Review E, 95,032701. doi:10.1103/PhysRevE.95.032701