Quasicritical behavior of the low-frequency dielectric permittivity in theisotropic phase of liquid crystalline materials - art. no. 052701

Results presented give evidence of the existence of quasicritical, fluidlik e behavior in the isotropic phase of 4-cyano-4-pentyl-biphenyl (5CB) for fr equencies ranging from the static to the ionic-dominated [low-frequency (LF )] region. Despite the boost of dielectric permittivity on lowering the fre quency below 1 kHz, values of the isotropic-nematic transition discontinuit y (approximate to1.1 K) and the critical exponent alpha (approximate to0.5) remain constant. It is shown that the contribution from residual ionic imp urities is a linear function of temperature in the critical, prenematic flu ctuation-dominated region. The validity of the fluidlike and critical behav ior for LF dielectric permittivity confirmed results of a derivative analys is of the experimental data: d epsilon /dT proportional to (T -T*)(-alpha), originally proposed for critical mixtures. Results of a preliminary test i n the isotropic phase of 4-decyl-4'-isothiocyanatobiphenyl (10BT), on appro aching the smectic-E phase, may indicate a general validity of results obta ined.