Heterogeneous Nanocomposite Materials Based on Liquid Crystals and Porous Media

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.

Dynamics of Ferroelectric and Nematic Liquid Crystals Confined in Porous Matrices

1994 ◽  
Vol 366 ◽  
Author(s):  
Fouad M. Aliev
Keyword(s):  
Liquid Crystals ◽  
Heterogeneous Media ◽  
Volume Fraction ◽  
Low Frequency ◽  
Pore Wall ◽  
Polar Molecules ◽  
Average Pore ◽  
Surface Polarization ◽  
The Difference ◽  
Frequency Relaxation

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.

Molecular Dynamics of Monomer, Oligomer, and Polymer Liquids in Porous Media: A Field-Cycling Nmr Relaxometry and NMR Field-Gradient Diffusometry Study

1994 ◽  
Vol 366 ◽  
Author(s):  
R. Kimmich ◽  
S. Stapf ◽  
R.-O. Seitter ◽  
P. Callaghan ◽  
E. Khozina
Keyword(s):  
Molecular Dynamics ◽  
Porous Media ◽  
Field Gradient ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Porous Matrix ◽  
Spin Lattice Relaxation ◽  
Nmr Relaxometry ◽  
Lévy Walks ◽  
Field Cycling

ABSTRACTThe molecular dynamics of fluids in porous media has been studied using field-cycling NMR relaxometry and NMR field-gradient diffusometry. The frequency dependences of the 1H and 2H spin-lattice relaxation times T1 of various liquids in porous glass reveal weak and strong adsorption behaviour depending on the polarity of the adsorbates. Correlation times eight orders of magnitude longer than in bulk have been observed. The T1 dispersion moreover reflects geometrical details of the matrix in a length scale three orders of magnitude longer than the adsorbate molecules. The mean-square displacements of adsorbate molecules on the surface are only one order of magnitude less than in bulk. The global diffusivity is reduced by tortuosity and porosity effects. The observed phenomena may be explained by bulk-mediated surface diffusion, i.e., Lévy walks. The dynamics of polymer chains much longer than the pore size is characteristicly different from that in bulk melts. There is evidence that the reptation mechanism explains at least a part of the phenomena observed for the porous matrix in contrast to findings with bulk polymer melts.

Heterogeneous Microcomposite Materials Based on Porous Matrices and Liquid Crystals

1996 ◽  
Vol 431 ◽  
Author(s):  
F. M. Aliev ◽  
G. P. Sinha
Keyword(s):  
Liquid Crystals ◽  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Physical Properties ◽  
Wide Spectrum ◽  
Relaxation Times ◽  
Average Pore ◽  
Relaxational Process ◽  
Porous Matrices ◽  
Interconnected Pores

AbstractHeterogeneous microcomposite materials based on porous matrices with randomly oriented, interconnected pores (porous glasses with average pore sizes of 100 Å and 1000 Å) and parallel cylindrical pores (Anopore membranes with pore diameters of 200 Å and 2000 Å) impregnated with liquid crystals (LC) were investigated by dynamic light scattering and dielectric spectroscopy. The physical properties of confined LC are very different from that of the bulk. One of the new properties among others observed for LC confined in porous matrices is the slow relaxational process which does not exist in the bulk LC and a wide spectrum of relaxation times (10−8 – 10)s which were established in both dynamic light scattering and dielectric experiments. We found that for LC dispersed in porous matrices with randomly distributed interconnected pores, the contribution to physical properties and observed behavior from interfacial layers dominates and almost completely determines low frequency relaxational process.

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

2016 ◽  
Vol 4 (16) ◽  
pp. 3485-3491 ◽  
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.

Slow Dynamics and Glass-Like Behavior of Liquid Crystals Dispersed in Nanoporous Media

1996 ◽  
Vol 455 ◽  
Author(s):  
F. M. Aliev ◽  
G. P. Sinha
Keyword(s):  
Liquid Crystals ◽  
Relaxation Times ◽  
Time Range ◽  
Slow Mode ◽  
Photon Correlation ◽  
Nanoporous Media ◽  
Cylindrical Pores ◽  
Relaxational Process ◽  
Porous Matrices ◽  
Interconnected Pores

ABSTRACTWe have investigated the dynamic behavior of liquid crystals (LC), which are not glass formers when in bulk form, confined in porous matrices with randomly oriented, interconnected pores as well as in parallel cylindrical pores with different pore sizes by photon correlation (time range: 20 ns-103s) and dielectric spectroscopies (frequencies: 0.1 Hz-1.5GHz). We observed that in random pores (pore size is 10 nm and 100 nm) LC does not crystallize at temperatures about 25° C below bulk crystallization temperature and the non-Debye relaxational processes studied by both photon correlation and dielectric experiments were found not to be frozen. Slow relaxational process which does not exist in bulk LC and a broad spectrum of relaxation times (10−8 − 10)s appear not only for LC in random pores but in cylindrical pores as well. However in matrices with random pores of 100 Å, glass-like behavior of slow mode (τ > 1ms) was observed. The relaxation time (determined in photon correlation experiment) of this slow process strongly increases when temperature decreases from 300 K up to 270 K varying from 0.2ms to 14 s and it's temperature dependence is described by the Vogel-Fulcher law.

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.

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