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-40-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 .T/ D c.T 􀀀 TC/􀀀 . In the immediate vicinity of the I–N transition a novel anomaly has been found: 1 / 1=.T 􀀀 T /, where T is the temperature of the virtual continuous transition and 1 is the excess over the ‘background behavior’. Experimental results are confronted with the comprehensive Landau–de Gennes theory based modeling.