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

Article: Nonlinear dielectric effect in the isotropic phase above theisotropiccholesteric 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. · 1.96 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The results presented give the evidence for the quasicritical, pretransitional behavior of dielectric properties in the isotropic phase of a rodlike nematic liquid crystal with the transverse permanent dipole moment. Studies were conducted in 2cyano4pentylbiphenyl 4(trans4pentylcyclohexyl) benzoate, focusing on the staticand ionicdominated lowfrequency (LF) regions. For the static dielectric permittivity [epsilon(')(T)] the application of the derivative analysis revealed the pretransitional anomaly associated with the specific heat exponent alpha approximately 0.5. For the LF domain the contribution to epsilon(')(T) from residual ionic impurities follows a linear temperature dependence on approaching the isotropicnematic (IN) transition. This dependence and pretransitional anomalies of electric conductivity and dielectric modulus can be associated with the influence of prenematic fluctuations. "Linear" dielectric studies were supported by the static nonlinear dielectric effect measurements, which delivered reliable estimations of the temperature of the hypothetical continuous phase transition T(*) and the discontinuity of the IN transition DeltaT approximately 1.7 K.The Journal of Chemical Physics 05/2006; 124(14):144907. · 3.12 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
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