Nematic Phases in 1,2,4-Oxadiazole-Based Bent-Core Liquid Crystals: Is There a Ferroelectric Switching?
Article first published online: 7 FEB 2012
Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Advanced Functional Materials
Volume 22, Issue 8, pages 1671–1683, April 24, 2012
How to Cite
Shanker, G., Nagaraj, M., Kocot, A., Vij, J. K., Prehm, M. and Tschierske, C. (2012), Nematic Phases in 1,2,4-Oxadiazole-Based Bent-Core Liquid Crystals: Is There a Ferroelectric Switching?. Adv. Funct. Mater., 22: 1671–1683. doi: 10.1002/adfm.201101770
- Issue published online: 13 APR 2012
- Article first published online: 7 FEB 2012
- Manuscript Revised: 24 NOV 2011
- Manuscript Received: 31 JUL 2011
- nematic liquid crystals;
- electro-convection patterns;
- bent-core mesogens;
Four series of new 1,2,4-oxadiazole derived bent-core liquid crystals incorporating one or two cyclohexane rings are synthesized and investigated by optical polarizing microscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), electro-optical, and dielectric investigations. All the compounds exhibit wide ranges of nematic phases composed of tilted smectic (SmC-type) cybotactic clusters with strongly tilted aromatic cores (40–57°) and show a distinct peak in the current curves observed under a triangular wave field. Dielectric spectroscopy of aligned samples corroborates the previously proposed polar structure of the cybotactic clusters and the ferroelectric-like polar switching of these nematic phases. Hence, it is shown that this is a general feature of the nematic phases of structurally different 3,5-diphenyl-1,2,4-oxadiazole derivatives. In these uniaxial nematic phases there is appreciable local biaxiality and polar order in the cybotactic clusters. As a second point it is shown that electric field induced fan-like textures, as often observed for the nematic phases of bent-core liquid crystals, do not indicate the formation of a smectic phase, rather they represent special electro-convection patterns due to hydrodynamic instabilities.