Submicrosecond Preliminary Process of Electric-Field-Induced Reorientation of a Ferroelectric Liquid Crystal, 5-(2-Fluoroalkoxy)-2-(4-n-Alkylphenyl)-Pyrimidine, Studied by Time-Resolved Infrared Spectroscopy

Abstract

Pulsed electric-field-induced reorientation of a ferroelectric liquid crystal (FLC), 5-(2-fluorooctyloxy)-2-(4-hexylphenyl)-pyrimidine, has been investigated by using a dispersive submicrosecond time-resolved infrared spectroscopic technique. The observed absorbance decay for a band at 1440 cm−1 due to a ring-stretching mode of the phenylpyrimidine group indicates that the FLC molecule reorients from a stationary state with a slight delay (less than 1 μs) just after the upswing of the electric field, while counter-reorientation occurs with a delay time of a microsecond after the reverse of the electric field. The delay time for the counter-reorientation changes with temperature, indicating that the viscosity has a strong influence on the delay time. It is also indicated in the present study that the whole FLC molecule reorients simultaneously as a rigid rod in both the preliminary and the counter-reorientation process.

Reorientation of Nematic Liquid-Crystals and Liquid-Crystalline Polymers in an Electric Field Studied by FT-IR Time-Resolved Spectroscopy and 2D-Correlation Analysis

“…12 The same effect was observed for FLC in the region of negative P s , 17 whereas for P s > 0 there is a very weak influence of the field strength on the rate of reorientation. 17,21 Significant progress in the understanding of the electric-fieldinduced structural changes of LCs was made by introduction of two-dimensional (2D) correlation analysis to the infrared spectra by Noda. [22][23][24] At first, the method was applied in studies of polymers subjected to a small amplitude sinusoidal mechanical perturbation.…”

“…17,21 It was found for 5CB that the relaxation time of the rise and decay processes decreased with increasing field strength. 12 The same effect was observed for FLC in the region of negative P s , 17 whereas for P s > 0 there is a very weak influence of the field strength on the rate of reorientation. 17,21 Significant progress in the understanding of the electric-fieldinduced structural changes of LCs was made by introduction of two-dimensional (2D) correlation analysis to the infrared spectra by Noda.…”

“…[8][9][10][11] Other authors reported that the core of 5CB and other LCs responds more sensitively to the electric field than the flexible part. [12][13][14] On the other hand, no differences were found for 5CB and other LCs; [15][16][17] the possible explanation for this disagreement was given elsewhere. 18 In the case of ferroelectric liquid-crystalline polymer, it was proposed that not only the mesogen but also the spacer and at least part of the backbone participate in the reorientation process; 19 however, 2D-correlation analysis for the same sample did not support this conclusion.…”

Time-Resolved Fourier-Transform Infrared Spectroscopy on the Inter- and Intramolecular Orientational Dynamics in Ferroelectric Liquid Crystalline Dimers

“…Until recently, the molecular orientation has been followed as the changes in the intensity of IR bands, with the polarization of the incident beam being fixed [1][2][3][4][5][6]. The interpretation of these results is ambiguous because this procedure requires assumptions about the orientational distribution functions for different molecular segments and their tilting angles.…”

Molecular Dynamics at Electrical- and Optical-Driven Phase Transitions: Time-Resolved Infrared Studies Using Fourier-Transform Spectrometers

“…This is repeated after the mirror has moved to the next position, eventually composing the complete interferogram. The step-scan technique is mainly applied in biophysics and polymer chemistry where, for instance, the photolysis processes of chemical reactions [9], bacteria systems [10,11,12,13,14] and the time-dependent reorientation of liquid crystals under the influence of a short electric field [15,16,17,18,19] are studied. But also temperature-and light-induced phase transitions can be investigated [20,21].…”