2012 Impact factor 1.824
EPJ E - Soft Matter and Biological Physics
Soft Matter and Biological Physics


Eur. Phys. J. E 7, 387-392 (2002)
DOI: 10.1140/epje/i2001-10097-3

Glassy and fluidlike behavior of the isotropic phase of n-cyanobiphenyls in broad-band dielectric relaxation studies

S.J. Rzoska1, M. Paluch1, A. Drozd-Rzoska1, J. Ziolo1, P. Janik1 and K. Czuprynski2

1  Institute of Physics, University of Silesia, Uniwersytecka 4, 40-007 Katowice, Poland
2  Military Technical University, ul. S. Kaliskiego, Warsaw, Poland

rzoska@us.edu.pl

(Received 22 November 2001)

Abstract
It is shown that the temperature behavior of peaks $\left( f_p,\varepsilon
_p^{\prime\prime}\right) $ of dielectric loss curves in the isotropic phase of n-cyanobiphenyls $\left( n=8,9,10\right) $ with isotropic-nematic and isotropic-smectic A transitions exhibits features characterisic for both supercooled, glass-forming liquids and critical, binary mixtures. The behavior of $f_p\left( T\right) $ can be portrayed by the Vogel-Fulcher-Tamman relation and the "critical-like", mode-coupling theory (MCT) equation. The latter is supported by the novel analysis of electric conductivity $\sigma \left( T\right) $. The obtained $f_p\left( T\right) $ and $\sigma \left( T\right) $ dependencies can be related by using the fractional Debye-Einstein-Stokes law. For all tested mesogens the static dielectric permittivities $\varepsilon ^{\prime}\left( T\right) $ and $\varepsilon _p^{\prime\prime}\left( T\right) $ are described by dependencies resembling those applied in the homogeneous phase of critical mixtures but with specific-heat critical exponent $\alpha
\approx 0.5$ . This behavior agrees with the novel fluidlike description for the isotropic-nematic transition (P.K. Mukherjee, Phys. Rev. E 51, 5745 (1995); A. Drozd-Rzoska, Phys. Rev. E 59, 5556 (1999)). The obtained glassy features of dielectric relaxation support the recent simulation analysis carried out by M. Letz et al.  (Phys. Rev. E 62, 5173 (2000)).

PACS
64.70.Md - Transitions in liquid crystals.
64.70.Pf - Glass transitions.
64.60.Ht - Dynamic critical phenomena.


© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002