Distortion-sensitive insight into the pretransitional behavior of 4-n-octyloxy-4′-cyanobiphenyl (8OCB)

Abstract

Results of studies of the static and dynamic dielectric properties in rod-like 4-n-octyloxy-4'-cyanobiphenyl (8OCB) with isotropic (I)-nematic (N)-smectic A (SmA)-crystal (Cr) mesomorphism, combined with measurements of the low-frequency nonlinear dielectric effect and heat capacity are presented. The analysis is supported by the derivative-based and distortion-sensitive transformation of experimental data. Evidence for the I-N and N-SmA pretransitional anomalies, indicating the influence of tricritical behavior, is shown. It has also been found that neither the N phase nor the SmA phase are uniform and hallmarks of fluid-fluid crossovers can be detected. The dynamics, tested via the evolution of the primary relaxation time, is clearly non-Arrhenius and described via τ(T) = τ(c)(T-T(C))(-φ). In the immediate vicinity of the I-N transition a novel anomaly has been found: Δτ is proportional to 1/(T - T*), where T* is the temperature of the virtual continuous transition and Δτ is the excess over the 'background behavior'. Experimental results are confronted with the comprehensive Landau-de Gennes theory based modeling.

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB–N phase transition

“…This fact is perfectly explained by the proposed Landau model, and it shows a quantitative difference with what we obtain for binary mixtures showing the SmA-N phase transition. For the systems we have studied, 39,[47][48][49] the SmA-N transition may be secondorder, but the associated heat capacity peaks are well defined as observed in the experimental measurements.…”

“…This is an important difference with those binary phase diagrams exhibiting the SmA-N phase transition where the transitional entropy decreases as the nematic range increases but the heat capacity peak associated with the SmA-N phase transition is not suppressed even when the transitional entropy is very small or zero. 39,[47][48][49] Fig . 4 shows the K 3 and K 1 elastic constants for pure FFO9OCB and CB7CB and three selected binary mixtures as a function of the shifted temperature, T À T N TB -N , in the N-phase.…”

Impact of ferroelectric and superparaelectric nanoparticles on phase transitions and dynamics in nematic liquid crystals

“…The DSE relations (S = 1, translational -orientational coupling) converts into the fractional Debye -Stokes -Einstein (FDSE) relation for S ≠ 1 4,17,19 .…”

Impact ofBaTiO3nanoparticles on pretransitional effects in liquid crystalline dodecylcyanobiphenyl

“…In the nematic phase measurements of the dielectric constant constitute a basic tool for determining the behavior of the order parameter. The successful parametrization of the pretransitional anomaly for I-N and I-SmA transitions is possible [32][33][34][35][36]:…”

“…It covers only the case of the I N  transition where the pretransitional anomaly was detected for the behavior of the diameter, namely [35] : T is the temperature metric of the discontinuity for this transition.…”