Linear and non-linear dielectric pretransitional behavior near the isotropic-nematic phase transition for 4-cyano-4-n-pentylbiphenyl (5CB)

Linear and non-linear dielectric permittivity measurements for n-pentylcyanobiphenyl 5CB are presented. 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 influence of the pretransitional behavior on the dynamic properties above and below the nematic clearing temperature (TJ-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 beta(CD) drops on approaching the clearing temperature. This is connected with the broadening of the dielectric absorption width.