Electro -optical and dielectric properties of ferroelectric liquid crystals formed by banana -shaped molecules.

摘要

Using polarizing microscope, differential scanning calorimetry, X-ray diffraction and dielectric spectroscopy, we have characterized the electro-optical and dielectric properties of achiral swollen banana-shaped materials, chiral banana-shaped liquid crystals and photoactive achiral banana-shaped liquid crystals, respectively. By dissolving non-polar solvents (xylene and hexadecane) into a banana-shaped ferroelectric liquid crystal, we have lowered the isotropic-mesophase transition temperature from 125°C to 70°C and widened the switching temperature range from ∼2°C to ∼50°C (i.e., room temperature switching). Then we have investigated the electro-optical and dielectric properties of four chiral banana-shaped molecules that contain chiral centers. Compared to their achiral counterparts, these chiral banana-shaped ferroelectric liquid crystals have exhibited quite different electro-optical and dielectric properties such as linear temperature dependence of the polarization. Finally, we have studied the effect of photo-irradiation on the electro-optical properties of banana-shaped FLC with built-in azo-linkage. Our results show that both the polarization and the structures of polarization current curves have been modified upon photo-irradiation. We have discussed the mechanisms that are responsible for the changes in the electro-optical properties of these ferroelectric liquid crystals; more specifically we have interpreted the linear temperature dependence of polarization in the light of Landau-de Gennes theory.