Application of Broad-Band Dielectric Spectroscopy for Investigations of Liquid Crystal - Porous Media Microcomposites

1997 ◽  
Vol 500 ◽  
Author(s):  
G. P. Sinha ◽  
B. Batalla ◽  
F. M. Aliev
Keyword(s):  
Dielectric Properties ◽  
Dielectric Spectroscopy ◽  
Volume Fraction ◽  
Broad Band ◽  
Interfacial Polarization ◽  
Pore Wall ◽  
Slow Process ◽  
Frequency Range ◽  
Average Pore ◽  
Hindered Rotation

ABSTRACTWe applied ultra broad-band dielectric spectroscopy in the frequency range from 10–3 Hz to 109 Hz to investigate the effect of size, shape and volume fraction of the pores in the porous matrices on the dielectric properties of liquid crystals (LC) dispersed in these matrices. Measurements in such a broad frequency range make it possible to obtain detailed information on the important aspects of the electrical behavior of heterogeneous materials such as: conductivity, surface polarization, and influence of confinement on dynamics of molecular motion of polar molecules forming LC. We investigated alkylcyanobiphenyls in the isotropie, nematic and smectic phases dispersed in porous glasses (average pore sizes - 100 Å and 1000 Å) which have randomly oriented, interconnected pores, and anopore membranes (pore diameters - 200 Å and 2000 Å) with parallel cylindrical pores. Dispersion of LC resulted in qualitative changes of their dielectric properties. Analysis of broad-band dielectric spectra shows that in organic (LC) - inorganic (porous matrix) heterogeneous composites conductivity plays an important role at F <1 Hz. We observe the appearance of new dielectric modes: a very slow process with characteristic frequency ≃ (1 – 10) Hz and a second process in frequency range about (103 - 106) Hz. The slow process arises due to the relaxation of interfacial polarization at pore wall - LC interface. The origin of this could be due to absorption of ions at the interface. Another possibility is the preferential orientation of the permanent dipoles at pore surface. The second new mode is due to the hindered rotation of the molecules near the interface. Additionally we observed two bulk like modes due to the rotation of the molecules around their short and long axii which are modified.

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.

scholarly journals Dielectric Properties of Deep Ice Cores with Air-Hydrate Inclusions (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 210
Author(s):  
Shinji Mae ◽  
Takeo Hondoh ◽  
Masayoshi Nakawo ◽  
C.C. Langway
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
Dielectric Properties ◽  
Time Variation ◽  
Volume Fraction ◽  
Ice Cores ◽  
Frequency Range ◽  
Temperature Range ◽  
The Core

Air-hydrate inclusions have been found in deep ice cores from Dye 3, Greenland, which were taken in August 1981. Although the concentration of the air-hydrate crystals decreased with time, when the core was stored at a temperature of −50 °C, they still existed to an appreciable extent in 1985. An ice specimen was cut out from the Dye 3 core at a depth of 1500 m, where the volume fraction of the hydrate crystals was about 10−3 by volume. Its dielectric properties were measured in September 1985, in a frequency range of 30-20 × 103 Hz and temperature range of −20° to −90°C. The activation energy obtained for the relaxation time of the Debye dispersion was about 0.2 eV, which is much smaller than that of pure ice. The measurement was repeated once a month for about a year, and the sample was stored at a temperature of −10 °C between measurements. The time variation of the dielectric properties has been discussed in relation to the deterioration of the air-hydrate crystals.

Dielectric Spectroscopy of Nematic Liquid Crystal Confined in Random Porous Matrices

1995 ◽  
Vol 411 ◽  
Author(s):  
F. M. Aliev ◽  
G. P. Sinha
Keyword(s):  
Relaxation Time ◽  
Liquid Crystal ◽  
Melting Point ◽  
Dielectric Spectroscopy ◽  
Volume Fraction ◽  
Dielectric Behavior ◽  
Isotropic Phase ◽  
Polar Molecules ◽  
Average Pore ◽  
Porous Matrices

ABSTRACTWe performed dielectric spectroscopy measurements to study dynamics of dielectrically active modes of nematic liquid crystals (LC) 5CB with polar molecules confined in silica porous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%). In the nematic phase of bulk 5CB there is only one mechanism of dielectric relaxation: rotation of polar molecules around short molecular axis with relaxation time τ ∼10−8s. The spatial confinement and the existence of a highly developed interphase have a strong influence on dielectric properties of LC. We found that at temperatures about 30°C below the bulk melting point in both porous matrices the dielectric behavior of confined liquid crystal is very different from the behavior expected for solid state. The dielectric modes were not frozen in both porous matrices and we observed four well defined relaxational processes with relaxation times τ1 ∼ 10−1s, τ2 ∼10−5s, τ3 ∼10−8s (bulk like) and τ3 ∼10−9s. These four processes do not vanish even at temperatures corresponding to deep bulk isotropic phase. The relaxation time of the first process (slow) shows glass-like behavior in a wide temperature range below bulk melting point.

Preparation and Dielectric Properties of Cu/PVDF Composite Films

2014 ◽  
Vol 1035 ◽  
pp. 417-421 ◽  
Author(s):  
Jian Wen Zhai ◽  
Ya Jun Wang ◽  
Jian Lou Deng ◽  
Chang Gen Feng
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Room Temperature ◽  
Volume Fraction ◽  
Composite Films ◽  
Interfacial Polarization ◽  
Dielectric Constants ◽  
Pvdf Film ◽  
Continuous Increase ◽  
Better Than

nanoand micro size Cu were employed separately and investigated comparatively. Different volume fraction of Cu was added into PVDF film in order to investigate the content of filler effect on the dielectric properties of polymer composites. XRD and SEM were used to analyze the crystalline phase and microstructure of the films. The results show that two sizes of Cu have the same peak features, and with the continuous increase of the content of Cu, it disperse better in PVDF. The dielectric constant (ε) of the composite containing 16 vol% micro-CCTO filler is 16 at 100 Hz and room temperature, and its dielectric loss (tanδ) is only 0.15, which is substantially better than others. Besides, for 18 vol% nanoCu/PVDF composite tanδis 0.25 andεis 18 at 100 Hz. Moreover,εand tanδof nanoCu/PVDF composite are both higher than those of micro-Cu/PVDF. Analysis shows that the composites with nanoCu have higher dielectric constants, which is mainly from the interfacial polarization.

Polarization Measurements of Molded Liquid Crystal Polymer/Titania Composites

2010 ◽  
Author(s):  
B. R. Dantal ◽  
A. Saigal ◽  
M. A. Zimmerman
Keyword(s):  
Refractive Index ◽  
Liquid Crystal ◽  
Dielectric Properties ◽  
Millimeter Wave ◽  
Hybrid Materials ◽  
Broad Band ◽  
High Refractive Index ◽  
Liquid Crystal Polymer ◽  
Frequency Range ◽  
Crystal Polymer

During the past decade, the preparation of inorganic/organic hybrid materials with high refractive index has attracted considerable attention. In particular, TiO2 (Titanium dioxide or Titania), as inorganic domains, have been incorporated into a polymer matrix to produce high refractive index hybrid materials [1–3]. Polarization of injection molded liquid crystal polymer/Titania composite parts have been investigated in the broad band millimeter wave frequency range. The measurements have been performed by using two different spectroscopy techniques. First, free space quasi optical millimeter wave spectrometer, equipped with a high power source coherent radiation tunable in the 40–90 GHz frequency range is used. Second, low power dispersive Fourier transform spectrometer has been used for higher frequencies in the range of 100–600 GHz. Dielectric properties of liquid crystal polymer/Titania composites have been determined in the broad band millimeter wave frequency range. A correlation between dielectric properties and dispersed Titania weight percent has been observed using the two spectroscopy techniques. It is found that the absorption coefficient and loss tangent is a strong function of the output power of the sources of the incident radiation. On the other hand, refractive index and real permittivity values measured from both spectroscopy techniques are similar. In addition, it has been found that transmittance level and absorption losses depend on the orientation of the samples with respect to the orientation of electric and magnetic fields in the incident electro-magnetic wave. Finally, the polarization of the parts varies with the direction of flow of the molten plastic into the cavity.

scholarly journals Dielectric Properties of Deep Ice Cores with Air-Hydrate Inclusions (Abstract)

1988 ◽  
Vol 10 ◽  
pp. 210-210
Author(s):  
Shinji Mae ◽  
Takeo Hondoh ◽  
Masayoshi Nakawo ◽  
C.C. Langway
Keyword(s):  
Activation Energy ◽  
Relaxation Time ◽  
Dielectric Properties ◽  
Time Variation ◽  
Volume Fraction ◽  
Ice Cores ◽  
Frequency Range ◽  
Temperature Range ◽  
The Core

Air-hydrate inclusions have been found in deep ice cores from Dye 3, Greenland, which were taken in August 1981. Although the concentration of the air-hydrate crystals decreased with time, when the core was stored at a temperature of −50 °C, they still existed to an appreciable extent in 1985.An ice specimen was cut out from the Dye 3 core at a depth of 1500 m, where the volume fraction of the hydrate crystals was about 10−3 by volume. Its dielectric properties were measured in September 1985, in a frequency range of 30-20 × 103 Hz and temperature range of −20° to −90°C. The activation energy obtained for the relaxation time of the Debye dispersion was about 0.2 eV, which is much smaller than that of pure ice.The measurement was repeated once a month for about a year, and the sample was stored at a temperature of −10 °C between measurements. The time variation of the dielectric properties has been discussed in relation to the deterioration of the air-hydrate crystals.

scholarly journals Dielectric Properties of P(VDF-TrFE-CTFE) Composites Filled with Surface-Coated TiO2 Nanowires by SnO2 Nanoparticles

Polymers ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 85 ◽  
Author(s):  
Qilong Zhang ◽  
Zhao Zhang ◽  
Nuoxin Xu ◽  
Hui Yang
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
Vinylidene Fluoride ◽  
Volume Fraction ◽  
Sno2 Nanoparticles ◽  
Interfacial Polarization ◽  
Hybrid Structure ◽  
Precipitation Method ◽  
Tio2 Nanowires ◽  
Improved Performance

Nanocomposites containing inorganic fillers embedded in polymer matrices have exhibited great potential applications in capacitors. Therefore, an effective method to improve the dielectric properties of polymer is to design novel fillers with a special microstructure. In this work, a combination of hydrothermal method and precipitation method was used to synthesize in situ SnO2 nanoparticles on the surface of one-dimensional TiO2 nanowires (TiO2 NWs), and the TiO2NWs@SnO2 fillers well-dispersed into the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] polymer. Hybrid structure TiO2NWs @SnO2 introduce extra interfaces, which enhance the interfacial polarization and the dielectric constant. Typically, at 10 vol.% low filling volume fraction, the composite with TiO2NWs @SnO2 shows a dielectric constant of 133.4 at 100 Hz, which is almost four times that of polymer. Besides, the TiO2 NWs prevents the direct contact of SnO2 with each other in the polymer matrix, so the composites still maintain good insulation performance. All the improved performance indicates these composites can be widely useful in electronic devices.

Broad Band Microwave Dielectric Measurement of Liquids with an Open-Ended Coaxial Probe

2013 ◽  
Vol 333-335 ◽  
pp. 191-198
Author(s):  
Jia Ming Shi ◽  
Quirino Balzano ◽  
Christopher C. Davis
Keyword(s):  
Dielectric Properties ◽  
Broad Band ◽  
Dielectric Measurement ◽  
Network Analyzer ◽  
Frequency Range ◽  
Probe Technique ◽  
Microwave Dielectric ◽  
Coaxial Probe

The principles of the open-ended coaxial probe technique for the measurement of permittivity are described. Measurements of dielectric properties are carried out over a frequency range from 300MHz to 50GHz, with a system comprising an Agilent E8364B network analyzer and a connected 2.2mm diameter open-ended coaxial probe. Water, methanol and salines of 0.1M, 0.2M, 0.6M are used as calibration liquids or liquids to be measured. Measured permittivities are presented and compared with those calculated from the Cole-Cole equation. It is shown that, in order to get good results, the calibration liquid should be similar to the liquid being measured in dielectric properties.

scholarly journals Influence of Bi on dielectric properties of GaAs1−xBix alloys

2019 ◽  
Vol 37 (2) ◽  
pp. 244-248 ◽  
Author(s):  
K. Ulutas ◽  
S. Yakut ◽  
D. Bozoglu ◽  
D. Deger ◽  
M. Arslan ◽  
...  
Keyword(s):  
Optical Properties ◽  
Dielectric Properties ◽  
Space Charge ◽  
Dielectric Spectroscopy ◽  
Room Temperature ◽  
Frequency Range ◽  
Dielectric Characterization ◽  
Ionic Polarization

AbstractPure GaAs and GaAs1−xBix alloys with different Bi ratios (1 %, 2.5 %, 3.5 %) fitted with silver contacts were measured with a dielectric spectroscopy device. Dielectric characterization was performed at room temperature in the frequency range of 0.1 Hz to 1 MHz. GaAs exhibits three relaxation regions corresponding to space-charge, dipolar and ionic polarizations in sequence with increasing frequency while GaAs1−xBix samples show only a broad dipolar polarization in the same frequency range. This result proves the filling of the lattice with Bi through making a new bonding reducing the influence of ionic polarization. This finding supports the previous results concerning optical properties of GaAs1−xBix, presented in the literature.

scholarly journals Dielectric properties of silicosillenite crystals doped with chromium and manganese ions

2020 ◽  
Vol 28 (1) ◽  
pp. 25-28
Author(s):  
T. V. Panchenko ◽  
L. M. Karpova
Keyword(s):  
Dielectric Properties ◽  
Dielectric Spectroscopy ◽  
Sound Frequency ◽  
Manganese Ions ◽  
Frequency Range ◽  
Temperature Range

The effect of chromium and manganese ions on the dielectric properties of Bi12SiO20 crystals is studied by the dielectric spectroscopy methods in the sound frequency range in the temperature range 280 – 800 K.

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