Role of the Surface Interactions in Dynamics of 5*CB Molecules in Mixture with Al₂O₃ Grains as Studied by Dielectric Spectroscopy: Experimental Results

Abstract

Dielectric spectroscopy was used to determine both the real (e 0 ) and imaginary (e 00 ) parts of dielectric permittivity of a novel material, a mixture of liquid crystal 5 Ã CB and Al 2 O 3 powder. The main objective was to investigate the influence of surface on the molecular dynamics of 5 Ã CB. The high-frequency process was related to the reorientation of molecules around their short axes, the same results obtained for bulk 5 Ã CB. We find an additional low-frequency relaxation processes. This process was attributed to the surface polarization (molecules anchoring themselves to surface of Al 2 O 3 particles). The crystallization kinetics of cholesteric liquid crystal (LC) to the metastable crystalline phase was also studied.

The Universal Scaling of Dielectric Response as a Tool in the Description of a Complex Dynamic of 4′-Butyl-4-(2-methylbutoxy)azoxybenzene (4ABO5*)

“…, are about 87 [kJ/mol] and 10.7 [kJ/mol], respectively, and they coincide with the values reported in [26]. Obtained values of the activation energies are in agreement with the adequate ones reported for liquid crystals; for example, see [22,25,34,36,[48][49][50][51]. The deconvolution of the relaxation process around the short axis of the molecule into two component processes, shown in Figure 3b,d, is only an example distribution.…”

“…The temperature was controlled by a Quatro Novocontrol cryo system with temperature stability of 0.1K in both experiments. More experimental details (i.e., the description of the sample preparation and experimental setup) are given in [26,36]. The high-precision Novocontrol ALPHA analyzer and the high-frequency Agilent E4991 analyzer are suitable for measuring the dielectric response of polar liquid crystals; for example, see [22,33,[36][37][38][39][40][41][42][43].…”

Phase Behavior and Dynamics of the Liquid Crystal 4′-butyl-4-(2-methylbutoxy)azoxybenzene (4ABO5*)

“…The temperature dependence of the mean relaxation times for motions around the long and short axes is of the Arrhenius type with the values of the relaxation times and the activation enthalpies typical for these kind of substances. 1,[10][11][12][13]15 The temperature dependence of the relaxation time τ 1 in the crystalline phase can be described by VFT equation due to freezing slow collective motions of molecules 25 on approaching to T g ∼ 225 K. The ionic conductivity and the quantity proportional to the electric capacity are described by exponential functions of temperature. They are on the order of 10 −8 −10 −9 , in the liquid phases, which is typical for the liquid crystal substances.…”

Blocking of Phase Transitions in Liquid Crystal 5*CB (Isopentylcyanobiphenyl) as a Result of Surface Interactions in the Nanomembranes

“…Four clearly separated peaks in the curves tanδ(f, T) indicate the existence of four relaxation processes, while in the bulk of 5*CB are only two dynamic processes [6]. Increasing the number of dynamic processes is caused by the interaction of LC molecules with the walls of the pores [5,7,8]. Most significant difference is dramatic reduction in the amplitude of the all processes of relaxation during cooling at a temperature about 260K.…”