Dielectric studies of liquid crystals under high pressure. IV. Static permittivity and low frequency relaxation process in 4-n-hexyl-4′-cyanobiphenyl (6CB)

ABSTRACTWe performed dielectric spectroscopy measurements to study dynamics of collective modes of ferroelectric (FLC) and molecular motion of nematic (NLC) liquid crystals with polar molecules confined in silica macroporous and microporous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%) respectively. For FLC the Goldstone and the soft modes are found in macropores. The rotational viscosity associated with the soft mode is about 10 times higher in pores than in the bulk. These modes are not detected in micropores although low frequency relaxation is present. The last one probably is not connected with the nature of liquid crystal but is associated with surface polarization effects typical for two component heterogeneous media. The difference between the dynamics of orientational motion of the polar molecules of NLC in confined geometries and in the bulk is qualitatively determined by the total energy Fs of the interaction between molecules and the surface of the pore wall, which is found Fs ≈ 102erg/cm2.

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Dielectric studies under high pressure on strongly polar liquid crystals exhibiting monolayer smectic A phase

Thermochimica Acta ◽

10.1016/j.tca.2006.10.022 ◽

2007 ◽

Vol 452 (1) ◽

pp. 65-70 ◽

Cited By ~ 6

Author(s):

K.L. Sandhya ◽

D.S. Shankar Rao ◽

S. Krishna Prasad ◽

U.S. Hiremath ◽

C.V. Yelamaggad

Keyword(s):

High Pressure ◽

Liquid Crystals ◽

Polar Liquid ◽

Dielectric Studies ◽

Smectic A ◽

Smectic A Phase

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Heterogeneous Nanocomposite Materials Based on Liquid Crystals and Porous Media

MRS Proceedings ◽

10.1557/proc-457-431 ◽

1996 ◽

Vol 457 ◽

Author(s):

G. P. Sinha ◽

F. M. Aliev

Keyword(s):

Porous Media ◽

Liquid Crystals ◽

Relaxation Times ◽

Low Frequency ◽

Porous Matrix ◽

Nanocomposite Materials ◽

Smectic Liquid Crystals ◽

Porous Matrices ◽

Frequency Relaxation ◽

Quantitative Changes

ABSTRACTAn effective way of preparing a variety of liquid crystal based nanocomposite materials is to disperse LC in porous media with different porous matrix structure, pore size and shape. We present the results of investigations of quasiequilibrium and dynamical properties of nematic and smectic liquid crystals (LC) dispersed in porous matrices with randomly oriented, interconnected pores (porous glasses) and parallel cylindrical pores (Anopore membranes) by light scattering, photon correlation and dielectric spectroscopies. Confining LC to nanoscale level leads to quantitative changes in physical properties and appearance of new behavior which does not exist in either of the components. Relaxation of director fluctuations which is characterized by single relaxation time in the bulk LC are transformed to a process with a spectrum of relaxation times in pores, which includes extremely slow dynamics typical for glass formers. Existence of developed interface in these materials leads to new dielectric properties such as an appearance of a low frequency relaxation of the polarization and modification of dipole rotation.

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Nanoparticles dispersed in liquid crystals: impact on conductivity, low-frequency relaxation and electro-optical performance

Journal of Materials Chemistry C ◽

10.1039/c6tc00659k ◽

2016 ◽

Vol 4 (16) ◽

pp. 3485-3491 ◽

Cited By ~ 35

Author(s):

Martin Urbanski ◽

Jan P. F. Lagerwall

Keyword(s):

Liquid Crystals ◽

Dielectric Response ◽

Low Frequency ◽

Charge Carriers ◽

Host Material ◽

Optical Performance ◽

Mobile Charge ◽

Electro Optic ◽

Frequency Relaxation

We show how the contamination with mobile charge carriers caused by nanoparticle doping affects the dielectric response of a nematic host material and deteriorates its electro-optic performance.

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