Dielectric and elastic properties of fluorine-containing tricyclic isothiocyanate liquid crystal

ABSTRACT

The dielectric and elastic properties of liquid crystals (LCs) generally depend on the molecule structure, such as polar group and carbon chain length. For further investigation of the influence of molecular structure on the dielectric and elastic properties of fluorine-containing tricyclic isothiocyanate LC, the experimental temperature was controlled at 25°C by precision hot stage, and a precision LCR meter was used to measure the capacitance of six LC cells under the voltage from 0.1 to 20 V at 1 kHz. An LC cell capacitance model and a dual-cell model were adopted to obtain the dielectric anisotropy, and the capacitance–voltage curves of six LC materials were plotted. The threshold voltage of Fréedericksz transition was analysed, and a finite difference iterative method was used to attain specific values of three elastic constants. The influence of molecular structure on the dielectric and elastic constants was finally analysed. Experimental results showed that the introduction of meta-difluoro group would increase the dielectric anisotropy and reduce the threshold voltage of LC. As the length of the alkyl carbon chain increased, the dielectric anisotropy would have an odd–even alternation effect, which would lead to changes in the elastic constants of LC.

Graphical Abstract

KEYWORDS:

• LC cell capacitance model
• dual-cell model
• odd–even alternation effect
• dielectric anisotropy
• elastic constant

Acknowledgments

We appreciate Professor Zhiyong Zhang from Wuhan Polytechnic University for providing the LC materials.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [11374087,11504080]; Natural Science Foundation of Hebei Province [A2014202123, A2017202004]; Key Subject Construction Project of Hebei Province University; Research Project of Hebei Education Department [QN2014130, QN2015260]; Research and practice project of Hebei Province higher education and teaching reform [2017GJJG018]; Project of College Students Innovation and Entrepreneurship Training Program [20181008001, 201810080116].