Premium
Nematic Phases in 1 ,2,4‐Oxadiazole‐Based Bent‐Core Liquid Crystals: Is There a F erroelectric Switching?
Author(s) -
Shanker Govindaswamy,
Nagaraj Mamatha,
Kocot Antoni,
Vij Jagdish K.,
Prehm Marko,
Tschierske Carsten
Publication year - 2012
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201101770
Subject(s) - liquid crystal , materials science , differential scanning calorimetry , oxadiazole , phase (matter) , polar , dielectric , crystallography , optical microscope , bent molecular geometry , biaxial nematic , electric field , ferroelectricity , diffraction , condensed matter physics , optics , molecular physics , optoelectronics , scanning electron microscope , thermodynamics , organic chemistry , physics , composite material , chemistry , quantum mechanics , astronomy
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.