Electrohydrodynamic Instabilities in Nematic Liquid Crystals in Low‐Frequency Fields

1972 ◽  
Vol 20 (9) ◽  
pp. 337-339 ◽  
Author(s):  
Dietrich Meyerhofer ◽  
Alan Sussman
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Low Frequency

Reorientation of Director of Nematic Liquid Crystals, Doped with Azodyes, under Light and Low-Frequency Fields

2002 ◽  
Vol 375 ◽  
pp. 363-372 ◽  
Author(s):  
M. I. Barnik ◽  
S. A. Kharchenko ◽  
V. F. Kitaeva ◽  
A. S. Zolot'Ko
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Low Frequency

Dielectric Relaxation in Filled Nematic Liquid Crystals

1999 ◽  
Vol 559 ◽  
Author(s):  
G.P. Sinha ◽  
M. Kreuzer ◽  
F.M. Aliev
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Broad Band ◽  
Low Frequency ◽  
Slow Process ◽  
Hydrophobic Particles ◽  
Total Polarization ◽  
Tumbling Motion ◽  
Frequency Relaxation

ABSTRACTNematic liquid crystals filled with Aerosil particles are new heterogeneous materials important for different optoelectronic applications. These materials are suspensions of small silica particles, about 10-17 nm in diameter, dispersed in nematic liquid crystals. The particles are known to form a network structure dividing liquid crystal into domains with linear size approximately 250 nm. We used both hydrophilic and hydrophobic particles, filling them with the nematic liquid crystal-5CB.Broad band dielectric spectroscopy (1 mHz - 1.5 GHz) was applied for the investigation of these materials. Two bulk-like modes due to the rotation of molecules around the short axis and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and the dispersion of dielectric permittivity due to conductivity were also observed. The modification of the surface of the particles has stronger influence on the slow process and is less important for the molecular modes. The contribution of the slow process for the hydrophilic sample to the total polarization is greater than for the hydrophobic sample. In addition, the corresponding characteristic frequencies are lower for the case of hydrophilic samples. These facts suggest that the low frequency relaxation is an Aerosil particle-liquid crystal interface related phenomena and the origin of this process maybe explained on the basis of surface induced polarization.

Broad-Band Dielectric Spectroscopy of Liquid Crystals Confined in Random and Cylindrical Pores

1996 ◽  
Vol 464 ◽  
Author(s):  
G.P. Sinha ◽  
F.M. Aliev
Keyword(s):  
Liquid Crystals ◽  
Dielectric Spectroscopy ◽  
Dynamic Properties ◽  
Nematic Liquid Crystals ◽  
Broad Band ◽  
Low Frequency ◽  
Molecular Rotation ◽  
Retardation Factor ◽  
Short Axis ◽  
Cylindrical Pores

ABSTRACTUsing dielectric spectroscopy in the frequency range 0.1 Hz-1.5 GHz, we investigated the influence of confinement on the dynamic properties of polar nematic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different, pores sizes. The confinement has a strong influence on the dielectric properties of LC which resulted in the appearance of a low frequency relaxational process (f ≤ 10 KHz) absent in bulk and a strong modification of modes due to the molecular rotation around short axis and librational motion. The differences between bulk and confined behavior are: (a) - the dielectrically active modes in confined LC are not frozen even at temperatures about 20 degrees below the bulk crystallization temperature; (b) - in the temperature range corresponding to the anisotropie phase in pores, lnτ, where τ is the relaxation time corresponding to the molecular rotation around short axis, is not a linear function of 1/T and there is an evidence for smectic type order formation at sufficiently low T; (c) - the retardation factor g = τ/τis is ≃ 1.5, where as the typical value of g in bulk nematic liquid crystals is ≃ 4; (d) - smooth and small changes in T at phase transition in pores suggest that the “isotropie” phase of LC in pores is not bulk like isotropie phase with complete disorder in molecular orientations, and some degree of orientation order still persists.

scholarly journals Dopant Effect and Cell-Configuration-Dependent Dielectric Properties of Nematic Liquid Crystals

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Feng-Ching Lin ◽  
Po-Chang Wu ◽  
Bo-Ru Jian ◽  
Wei Lee
Keyword(s):  
Carbon Nanotubes ◽  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Diffusion Constant ◽  
Low Frequency ◽  
Dielectric Spectrum ◽  
Dramatic Decrease ◽  
Ionic Content ◽  
Low Resistivity ◽  
Impurity Ions

The dielectric polarizations induced by impurity ions in both high- and low-resistivity nematic liquid crystals (NLCs) were investigated. Upon adding carbon nanotubes (CNTs) as a dopant, the former showed no distinct change in the low-frequency (< 102 Hz) dielectric spectrum, whereas the latter exhibited dramatic decrease in dielectric constant in that the CNTs remarkably trapped the impurity ions in the NLC of high ionic content. Consequently, the dopant raised the voltage holding ratio by 26% and prolonged the lifetime of the cell. Also investigated were ionic behaviors in the low-resistivity NLC confined in cells with three different configurations. The diffusion constant of the ions in homeotropic cells was found to be the greatest, and the dc conductivity, determined by the diffusion constant, was also higher in the homeotropic ones.

Dielectric Properties of Nematic Liquid Crystals in Low Frequency Regime

1995 ◽  
Vol 262 (1) ◽  
pp. 249-255 ◽  
Author(s):  
Hiroyoshi Naito ◽  
Yoshihisa Yokoyama ◽  
Shuichi Murakami ◽  
Masahiro Imai ◽  
Masahiro Okuda ◽  
...  
Keyword(s):  
Liquid Crystals ◽  
Dielectric Properties ◽  
Nematic Liquid Crystals ◽  
Low Frequency ◽  
Frequency Regime

The electrohydrodynamic instability in twisted nematic liquid crystals

1994 ◽  
Vol 4 (2) ◽  
pp. 239-252 ◽  
Author(s):  
A. Hertrich ◽  
A. P. Krekhov ◽  
O. A. Scaldin
Keyword(s):  
Liquid Crystals ◽  
Nematic Liquid Crystals ◽  
Electrohydrodynamic Instability ◽  
Twisted Nematic
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