Twin nematic phenylbenzoates in a.c. electric fields
作者:
ATSUSHI SHIOTA,
HILMAR KORNER,
CHRISTOPHER K. OBER,
期刊:
Liquid Crystals
(Taylor Available online 1998)
卷期:
Volume 25,
issue 2
页码: 199-206
ISSN:0267-8292
年代: 1998
DOI:10.1080/026782998206344
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
The orientational behaviour of nematic compounds having twin phenylbenzoate mesogens was examined under a wide range of a.c. electric fields (0-2 V mum-1 and 10Hz-50 kHz). For this study, crossed polarizing optical microscopy (POM) and real-time X-ray diffraction (RTXRD) measurements were employed to investigate optical and orientational response. These nematic compounds have a positive dielectric anisotropy and a relatively low epsilon// relaxation frequency which allowed study in both homeotropic and planar orientations over a controllable frequency range. The optical behaviour and X-ray results corresponded well, providing a tool for understanding the orientational behaviour of these liquid crystals. For homeotropic alignment, an electric field of over 1 V mum-1 was required in order to obtain good orientation. However, homeotropic orientation depended on a delicate balance between thermal fluctuations and dielectric torque imposed by the electric field, which are both strongly related to the elasticity of the LC domains. Due to this effect, the highest orientation parameter achieved for homeotropic orientation was only 0.48, which indicated that this state was still non-equilibrium. On the other hand, for planar orientation, a uniform texture with orientation parameter of 0.65 was easily obtained even at electric fields as low as 0.2 V mum-1. The application of an electric field stronger than 1 V mum-1 induced a distortion in the texture, and reduced the orientation parameter to 0.45 for planar alignment.
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