Article

# Quasicritical behavior of the low-frequency dielectric permittivity in the isotropic phase of liquid crystalline materials.

August Chelkowski Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland.

Physical Review E (Impact Factor: 2.31). 06/2001; 63(5 Pt 1):052701. DOI: 10.1103/PhysRevE.63.052701 Source: PubMed

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**ABSTRACT:**Results of the extended Landau-de Gennes model analysis and experimental studies of the isotropic-nematic (I-N) and isotropic-smectic-A (I-SmA) phase transitions in rod-like liquid crystalline n-alkylcyanobiphenyls are presented. Experiments were carried out as a function of temperature and pressure using the static dielectric permittivity and its 'nonlinear' (strong electric field related) counterpart-the low-frequency nonlinear dielectric effect. Precise estimations of the values of the discontinuity of the isotropic-mesophase transitions (ΔT) for nCB from n = 3-14 have been obtained. It is suggested that for each nCB a unique, characteristic minimal value of ΔT, associated with the I-N-SmA triple point, exists. For 'shorter' nCBs it can be hidden in the negative pressures domain. The possibility of the extension of the 'melting curve' into the negative pressures region as well as the appearance of the 'melting inversion' at high enough pressures is indicated.Journal of Physics Condensed Matter 07/2012; 24(37):375101. · 2.22 Impact Factor -
##### Article: Non-linear dielectric effect in the isotropic phase above the isotropic-cholesteric phase transition

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**ABSTRACT:**Using the Landau-de Gennes theory, the temperature, pressure and frequency dependence of the non-linear effect in the isotropic phase above the isotropic-cholesteric phase transition is calculated. The influence of pressure on the isotropic-cholesteric phase transition is discussed by varying the coupling between the orientational order parameter and the macroscopic polarization of polar cholesterics. Comparing the results of the calculations with existing data, we finally conclude that the model provides a description of the isotropic-cholesteric transition that takes all experimentally known features of the unusual negative and positive pretransitional effect in the isotropic phase of the system into account in a qualitatively correct way.Chemical Physics 12/2011; 389(1):64. · 1.96 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**Static and dynamic linear dielectric properties and shear viscosity of freely flowing 9CB in the isotropic (I), nematic (N) and smectic A (S(A)) phases were investigated. Pretransitional effects observed in the vicinity of the I to N phase transition manifest themselves as anomalies in the temperature dependence of the static permittivity, the rotational diffusion exponent and the activation energy of molecules rotating around their short axis. As a presmectic effect, a jump in the temperature dependence of the shear viscosity of freely flowing nematic 9CB is observed at about 0.5 °C before the transition to the S(A) phase.Journal of Physics Condensed Matter 02/2006; 18(6):1839-46. · 2.22 Impact Factor

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