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Paper
J. Mater. Chem., 2010, 20, 299 - 307, DOI: 10.1039/b914260f
The influence of an alkenyl terminal group on the mesomorphic behaviour and electro-optic properties of fluorinated terphenyl liquid crystals
Julita S. Gasowska, Stephen J. Cowling, Martin C. R. Cockett, Michael Hird, Robert A. Lewis, E. Peter Raynes and John W. Goodby
Novel liquid crystal terphenyls with two, three and four lateral fluoro substituents and an alkene unit at the end of a terminal chain are presented in terms of synthesis, mesomorphic behaviour and electro-optic properties. The difluoro analogues were found to exhibit the smectic C phase over a wide temperature range, with short temperature ranges of the smectic A and the nematic phase above. Very low melting points were recorded for the trifluoro analogues, and the shorter chain homologues of these materials exhibit the nematic phase over a wide temperatures with a monotropic smectic C phase and the higher homologues exhibit the smectic C phase over a wide temperature range with the nematic phase above. The tetrafluoroterphenyls exhibit the nematic phase over a wide temperature range with the complete absence of smectic phases. As appropriate, the materials were evaluated for dielectric anisotropy and threshold voltage in nematic phase, and mixed with a chiral dopant to evaluate the spontaneous polarisation, tilt angle and switching times in the chiral smectic C phase. The results show that these compounds are strong potential candidates for application in both vertically aligned nematic (VAN) and ferroelectric liquid crystal (FLC) devices.
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