Formation and development of nanometer-sized cybotactic clusters in bent-core nematic liquid crystalline compounds.

Yuri P Panarin,Sithara P Sreenilayam,Jagdish K Vij,Carsten Tschierske,Anne Lehmann

doi:10.3762/bjnano.9.121

Abstract

Two homologue achiral bent-core liquid crystals (LCs), BCN66 and BCN84, in their nematic phases are studied by dielectric spectroscopy in the frequency range 10 Hz–10 MHz. In each of these compounds, two relaxation processes are identified and assigned to (i) collective dynamics of molecules in nanometer-sized cybotactic clusters and (ii) individual molecular relaxations, in the ascending order of frequency of the probe field. The temperature and the bias electric field dependence of the dielectric strength and relaxation frequency for these processes are shown to give rise to sharpness in cluster boundaries, increased size and volume fraction in the LC nematic phase. The effect of the bias field on the LC cell is similar to reducing its temperature; both variables increase the cluster size and volume fraction and give rise to sharp cluster boundaries. The findings confirm that dielectric spectroscopy is a powerful and an extremely useful technique to provide a deeper understanding of the mechanism of cybotactic cluster formation in the isotropic liquid and the nematic phase of LCs as a function of temperature and the bias field.

Highlights

Biaxial liquid crystals (LCs) exhibit supramolecular structures with long-range orientational ordering of the long and the short molecular axes but without a long-range translational order
The bent-core nematic liquid crystals were previously investigated by dielectric spectroscopy for determining the elastic and viscosity constants [54], as well as the molecular dipole moment [55]
We investigated two nematic bent-core liquid crystals with the same mesogenic core and molar mass but with different alkyl terminal groups terminated by: (i) symmetrical C6H13 and (ii) asymmetrical with different groups C8H17 and C4H9 using dielectric spectroscopy in the nematic and isotropic phases

Summary

Introduction

Biaxial liquid crystals (LCs) exhibit supramolecular structures with long-range orientational ordering of the long and the short molecular axes but without a long-range translational order. The dielectric spectra of both bent-core nematic LCs were studied by cooling the aligned samples from their isotropic to nematic phases, whereby the results were rather similar with each other.

Results

Conclusion