| Summary: | 碩士 === 國立高雄師範大學 === 物理學系 === 90 === The properties of polarization and molecular dynamic behavior for six diastereomeric ferroelectric liquid crystals (FLCs) were investigated by the measurements of spontaneous polarization, tilt angles, and dielectric constants with or without a bias electric field. The results are helpful for establishing the relationship between the structure and the physical properties including their molecular dynamic behavior of them.
The influence of the structure on spontaneous polarization is obvious, especially the effect of the core structure. The value of the spontaneous polarization is increasing from biphenyl ring, naphthalene ring, to phenyl ring. The data of the tilt angles show that their Ps values of unit radius vary with their core structures. Dielectric measurements without bias electric field were carried out at temperatures for all phases. These dielectric spectra were analyzed in terms of Debye equation, Cole-Cole equation, and the correction of ionic conductivity at lower frequencies. In the fitting process, the sequential phase transitions of six samples could be reconstructed. The existence of ferrielectric phase (SmCγ＊) in the sample A and B whose core structures contain a phenyl ring is an unexpected finding. In addition, the dielectric measurement under a bias electric field at the ferroelectric phase for the compounds having an SR structure indicates that the Goldstone mode resulting from the fluctuation in the azimuthal angle shows two different kinds of behavior. The relaxation is increasing at first and then decreasing. In order to explaining this unusual behavior, a molecular structural fluctuating model is proposed in this study.
|
|---|
