Dielectric and XRD Investigation of Ferroelectric Liquid Crystal Composed of Banana-Shaped Achiral Molecules

Abstract

An achiral banana-shaped called F-490 liquid crystal has been examined by means of polarizing microscopy, differential scanning calorimetry (DSC) as well as X-ray diffraction (XRD) and dielectric spectroscopy methods. The phase diagram of the compound is proposed. The F-490 forms crystal-like phases the B₄ and the B₃ on heating and the banana-like antiferroelectric phase B₂ as well the B₃ and the B₄ phases on cooling. Moreover, the formation of solid phase depends upon thermal history. Dielectric studies have been done with HP set-up in a wide frequency range of 0.01–1.5 MHz using LINKAM 5 μm cells. Dielectric dispersion as well as absorption were calculated from the data. On the base these data the complex rotational dynamics of banana-shaped molecule have been described. The layer thickness and the unit cell parameters of B-phases were determined on the base of XRD results.

Keywords:

• banana-shaped molecules
• B_i phases
• dielectric spectroscopy
• X-ray diffraction

Acknowledgments

This work was supported in part by the Polish Ministry of Science and Informatization (Grant No. 1 P03 060 28). The authors would like to thank specially Professor W. Kuczyński and Dr. J. Hoffmann for help in the dielectric measurements and valuable discussions as well as Professor S. Wróbel for the reversal current measurements.