Article
Quasicritical behavior of the lowfrequency dielectric permittivity in the isotropic phase of liquid crystalline materials.
August Chelkowski Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40007 Katowice, Poland.
Physical Review E (Impact Factor: 2.33). 06/2001; 63(5 Pt 1):052701. DOI: 10.1103/PhysRevE.63.052701 Source: PubMed

Article: Nonlinear dielectric effect in the isotropic phase above the isotropiccholesteric phase transition
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ABSTRACT: Using the Landaude Gennes theory, the temperature, pressure and frequency dependence of the nonlinear effect in the isotropic phase above the isotropiccholesteric phase transition is calculated. The influence of pressure on the isotropiccholesteric 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 isotropiccholesteric 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. · 2.03 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: Results of the extended Landaude Gennes model analysis and experimental studies of the isotropicnematic (IN) and isotropicsmecticA (ISmA) phase transitions in rodlike liquid crystalline nalkylcyanobiphenyls 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) counterpartthe lowfrequency nonlinear dielectric effect. Precise estimations of the values of the discontinuity of the isotropicmesophase transitions (ΔT) for nCB from n = 314 have been obtained. It is suggested that for each nCB a unique, characteristic minimal value of ΔT, associated with the INSmA 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  [Show abstract] [Hide abstract]
ABSTRACT: This paper presents the results of measurements of the static and dynamic electric permittivity, the shear viscosity of a freely flowing sample, and the splay and bend elastic constants for 1(4transpropylcyclohexyl)2(4cyanophenyl)ethane (C3H7CyHxCH2CH2PhC=N) (3CCPE). The static permittivity of the isotropic phase shows prenematic critical behaviour which is discussed in the frame of the fluidlike model of Mukherjee. From the temperature dependence of the dielectric relaxation time (corresponding to the molecular rotation around the short axis) and the shear viscosity, the strength of the nematic potential and the effective length of the 3CCPE molecule (in the isotropic phase), were estimated. The splay and bend elastic constants were determined from the voltage dependence of the capacitance of a planar nematic cell.Liquid Crystals 08/2002; 29(9):12011207. · 2.35 Impact Factor
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