Dielectric spectroscopy of a smectic liquid crystal

Abstract

Complex dielectric spectroscopy (frequency range 5 Hz-13 MHz) has been used to analyse the frequency, temperature and bias-field dependences of the molecular dynamics of a very highspontaneous-polarization ferroelectric liquid crystalline material exhibiting SmA, SmC* and unknown SmX smectic phases. Different smectic phase transition temperatures have been observed from the study of the temperature dependence of the dielectric strength and the relaxation frequency. The phase transition temperatures (crystalline to isotropic phases) have also been described very accurately from the temperature-dependent symmetric and asymmetric shape parameters of the relaxation function and also the dc conductivity. In a planar aligned cell, two symmetric modes (Goldstone mode and domain mode) have been observed in both the SmX and SmC* phases. One asymmetric mode (X-mode) observed in the SmC* and SmA phases could be related to the interaction of dipoles of the ferroelectric liquid crystals being affected by the surface of the cell. The soft mode, which usually appears very close to the SmC*-SmA phase transition was not observed until the bias field was applied. The second order nature of the SmC*-SmA phase transition was revealed.

Spontaneous polarization and dielectric relaxation dynamics of ferroelectric liquid crystals derived from 2(S)-[2(S)-ethylhexyolxy] propionic acid and its (S, R)-diastereomer

“…According to Ref. [10], the domain mode (DM) contributed to relaxation at the frequency of about 10 kHz. The DM would not contribute to the high-frequency relaxation of FLCs in this study.…”

“…The one caused by large fluctuations in the azimuthal angle is the Goldstone mode (GM). The other, caused by small fluctuations in the tilt angle, is the soft mode (SM) [7][8][9][10][11][12][13]. For FLC compounds with a high degree of Ps, another type of collective dielectric process, known as the domain mode (DM), is a result of Ps under certain conditions.…”

A dynamical model for fractal and compact growth in supercooled systems

“…Nematic phases of bent-core molecules typically exhibit a higher viscosity and a slower relaxation dynamics of molecules than their calamitic nematic counterparts, with a difference of one to two orders of magnitude. The viscosity, relaxation frequency and relaxation time of a bentcore nematic phase are in the orders of 1 to 10 Pa·s [34], 10 5 to 10 6 Hz [29] and 1 to 10μs, respectively, where these values are comparable to those for fluid smectic phases of calamitic molecules [30][31][32]. Smectic phases of bent-core liquid crystals, such as the fractal-growing B2 phase ( figure 1(b)), typically exhibit a slower relaxation dynamics of molecules than their calamitic counterparts, with relaxation frequencies and relaxation times in the orders of 5×10 3 to 5×10 4 Hz [33] and 20 to 200μs, respectively.…”

“…For supercooled systems, a variety of patterns have been observed experimentally for the two-dimensional growth of liquid crystal phases out of an isotropic melt [24,25]. Apart from the typical growth of compact domains (figure 1(a)), irregular fractal percolation-like clusters (figure 1(b)) have been observed for a variety of liquid crystal phases [13][14][15][16][17][18][19][20][21] with a slow relaxation dynamics [26][27][28][29][30][31][32][33] and a large viscosity [30][31][32]34], where the corresponding mechanism of fractal growth remains to be understood.…”

Spontaneous Polarization and Dielectric Relaxation Dynamics of Two Novel Diastereomeric Ferroelectric Liquid Crystals

“…Dielectric relaxation in the chiral smectic C (SmC * ) phase occurs as a result of collective dielectric processes related to director reorientational motion and the molecular reorientation processes associated with the polarization of the molecules. The collective dielectric processes are mainly attributed to the Goldstone mode (GM) and the soft mode (SM) [7][8][9][10][11][12][13]. Moreover, for FLC compounds with a high degree of Ps, the domain mode (DM) exists.…”