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Linear and Non-linear Dielectric Pretransitional Behavior Near the Isotropic-nematic Phase Transition for 4-cyano-4-n-pentylbiphenyl (5CB)

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Linear and Non-linear Dielectric Pretransitional Behavior Near the Isotropic-nematic Phase Transition for 4-cyano-4-n-pentylbiphenyl (5CB)

G. Czechowski, J. Jadz˙yn, J. ZioΩo, S. J. Rzoskaa, and M. Palucha

Institute of Molecular Physics, Polish Academy of Sciences, ul. A. Smoluchowskiego 17, 60-179 Poznan´, Poland

aInstitute of Physics, Silesian University, Uniwersytecka 4, 40-007 Katowice, Poland Reprint requests to Prof. J. Z.; E-mail: ziolo@us.edu.pl

Z. Naturforsch. 57a, 244 – 246 (2002); received March 9, 2002

Linear and non-linear dielectric permittivity measurements for n-pentylcyanobiphenyl 5CB are pre- sented. By two different experimental methods the same value of the temperature discontinuity for the isotropic-nematic transition was obtained. Broadband dielectric relaxation tests showed a significant in- fluence of the pretransitional behavior on the dynamic properties above and below the nematic clearing temperature (TI–N). The form of the loss curves is clearly non-Debye’an and can be portrayed within the Cole–Davidson approximation (CD). In the isotropic and nematic phases the CD parameter bCDdrops on approaching the clearing temperature. This is connected with the broadening of the dielectric absorp- tion width.

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