Janik Malgorzata, Rzoska Sylwester J, Drozd-Rzoska Aleksandra, Zioło J, Janik Pawel, Maslanka Slawomir, Czupryński Krzysztof
Institute of Physics, Silesian University, ul. Uniwersytecka 4, 40-007 Katowice, Poland.
J Chem Phys. 2006 Apr 14;124(14):144907. doi: 10.1063/1.2185103.
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 2-cyano-4-pentylbiphenyl 4-(trans-4-pentylcyclohexyl) benzoate, focusing on the static-and ionic-dominated low-frequency (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 isotropic-nematic (I-N) 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 I-N transition DeltaT approximately 1.7 K.
所呈现的结果为具有横向永久偶极矩的棒状向列型液晶各向同性相中介电性质的准临界、预转变行为提供了证据。研究是在2-氰基-4-戊基联苯4-(反式-4-戊基环己基)苯甲酸酯中进行的，重点关注静态和离子主导的低频（LF）区域。对于静态介电常数[ε′(T)]，导数分析的应用揭示了与比热指数α约为0.5相关的预转变异常。对于低频区域，残余离子杂质对ε′(T)的贡献在接近各向同性-向列相（I-N）转变时呈现线性温度依赖性。这种依赖性以及电导率和介电模量的预转变异常可能与向列前涨落的影响有关。“线性”介电研究得到了静态非线性介电效应测量的支持，该测量给出了假设的连续相变温度T(*)以及I-N转变的不连续性ΔT约为1.7 K的可靠估计。
