Mesomorphic and dielectric properties of esters useful for formulation of nematic mixtures for dual frequency addressing system

2009 ◽  
Vol 17 (1) ◽  
Author(s):  
D. Ziobro ◽  
P. Kula ◽  
J. Dziaduszek ◽  
M. Filipowicz ◽  
R. DĄbrowski ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Homologous Series ◽  
Strong Dependence ◽  
Dielectric Anisotropy ◽  
Dual Frequency ◽  
Low Frequencies ◽  
High Frequencies ◽  
Smectic A ◽  
Smectic C ◽  
A Value

AbstractMesomorphic and dielectric properties of three homologous series of two and three ring fluorosubstituted esters are described. They are 4-cyano-3-fluorophenyl 4-alkyloxy-2-fluorobenzoates, 4-cyano-3-fluorophenyl 4-(4-alkylbenzoyloxy)-2-fluorobenzoates and 3-fluoro-4-cyanophenyl, or 3-fluoro-4-isothiocyanatophenyl or 3,4-difluorophenyl 4′-alkyl-2,3-difluoro-biphenyl-4-carboxylates. The compounds exhibit the nematic mesophase accompanied by the smectic A or smectic C mesophase in some cases. Most of them show strong dependence of the dielectric anisotropy Δε upon frequency, at low frequencies Δε reaches a value ∼200, while at high frequencies a small negative dielectric anisotropy appears.

NEAR STATIONARY DIELECTRIC PROPERTIES IN HALF-METALLIC FERROMAGNETIC Ag:CrO2 NANOCOMPOSITE PARTICLES AT HIGH FREQUENCIES

2008 ◽  
Vol 22 (14) ◽  
pp. 1423-1429 ◽  
Author(s):  
G. P. SINGH ◽  
S. RAM ◽  
A. K. THAKUR
Keyword(s):  
Dielectric Constant ◽  
Dielectric Properties ◽  
High Frequency ◽  
Power Loss ◽  
Room Temperature ◽  
Half Metallic ◽  
Nanocomposite Particles ◽  
High Frequencies ◽  
A Value ◽  
Ferromagnetic Particles

Nanocomposite particles of silver modified CrO 2 were synthesized by a chemical CrO 3 → CrO 2 reduction in the presence of Ag + in an aqueous medium whereby the half-metallic ferromagnetic particles of CrO 2 are generated within a shell of silver. The dielectric constant εr, AC resistivity ρAC, and the dielectric power loss were studied after annealing recovered Ag:CrO 2 powder (compacted as the billets), at 300°C for 2 h in air, at 10–1000 kHz frequencies (f) at room temperature. At 10 kHz, the ρr has as large a value as 49, with ρ AC = 106 k Ω-cm and power loss 0.42. As f increases, all the three parameters are decreased monotonically to the values 28, 3.6 kΩ-cm, and 0.06 respectively. Almost a steady εr as well as ρAC value exists, with controlled power loss, useful for high frequency applications over f ≥ 400 kHz .

scholarly journals A Basic Study on a Rectangular Plane Space Sound Absorber Using Permeable Membranes

2019 ◽  
Vol 11 (7) ◽  
pp. 2185 ◽  
Author(s):  
Sakagami ◽  
Okuzono ◽  
Somatomo ◽  
Funahashi ◽  
Toyoda
Keyword(s):  
Sound Absorption ◽  
Woven Fabrics ◽  
Absorption Coefficients ◽  
Basic Study ◽  
Low Frequencies ◽  
Permeable Membrane ◽  
High Frequencies ◽  
Single Leaf ◽  
A Value ◽  
Plane Space

In this communication, the sound absorption characteristics of rectangular-shaped plane space sound absorbers without any backing structure using permeable membranes (PMs) are measured by reverberation room method. First, three types of PMs, in this study woven fabrics, are selected with different flow resistances and surface densities. They are prepared in the plane rectangular-shaped space absorbers of two different sizes. The measured results are discussed through comparison with the existing theoretical and measured results for absorbers of the other shapes or configurations. The present results and discussion demonstrate that the reverberation absorption coefficients of the proposed absorbers are low at low frequencies and converge to a moderately high value at high frequencies. Especially, ones with higher flow resistance than the air impedance converge to a value greater than 0.5, which is a theoretically estimated maximum absorption coefficient of infinite single-leaf PM. This is inferred to be attributed mainly to area effect. From these results the proposed absorbers can be used effectively despite of their very simple structure. Also it is found that the proposed absorber can offer higher sound absorption than permeable membrane absorbers of other shapes or configuration. Regarding the effect of the size, the absorbers of smaller size offer higher absorption coefficients regardless of material properties of the PMs used in the experiments.

Dielectric Properties of Pd/Y8Z Composites

1999 ◽  
Vol 575 ◽  
Author(s):  
Mark G.H.M. Hendriks ◽  
Henk Verwei ◽  
Manon P. Timmerman
Keyword(s):  
Dielectric Properties ◽  
Percolation Threshold ◽  
Double Layer ◽  
Low Temperatures ◽  
Room Temperature ◽  
Electronic Conductivity ◽  
Impedance Measurements ◽  
High Frequencies ◽  
A Value ◽  
Double Layer Capacity

ABSTRACTImpedance measurements are performed on Pd/Y8Z composites. At 500 'C a 2- 108 times enhancement of the permittivity of the composite at a Pd composition near the percolation threshold for electronic conductivity relative to Y8Z at room temperature is obtained. At high frequencies, the enhancement decreases to a value comparable to geometric capacity of the composite as the double-layer capacity diminishes. At relatively low temperatures the capacity of Y8Z, due to ionic polarisability, increases with temperature.

scholarly journals Electro-Optical and Photo Stabilization Study of Nematic Ternary Mixture

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2283
Author(s):  
Aleksandra Kalbarczyk ◽  
Noureddine Bennis ◽  
Jakub Herman ◽  
Leszek R. Jaroszewicz ◽  
Przemysław Kula
Keyword(s):  
Liquid Crystal ◽  
Ternary Mixture ◽  
Liquid Crystal Displays ◽  
Dielectric Anisotropy ◽  
Driving Voltage ◽  
Dual Frequency ◽  
High Frequencies ◽  
High Birefringence ◽  
High Dielectric ◽  
Mesomorphic Properties

Liquid crystal materials composed of mixed nematic compounds find broad use in liquid crystal displays and photonic applications. A ternary mixture formed from three different nematic compounds shows peculiar behavior such as tunable electro-optical properties dependent on the frequency of the driving voltage. The paper presents an analysis of the response time and phase retardation of a frequency tunable nematic liquid crystal mixture (under code name 5005). This material possesses high birefringence (Δn = 0.32 at 633 nm) as well as high dielectric anisotropy (Δε = 6.3 at 100 Hz). The unique property of the 5005 mixture is frequency-controlled phase modulation, as in a dual frequency liquid crystal, while dielectric anisotropy goes to zero instead of being negative at high frequencies. For each component of the mixture, details on mesomorphic properties and their role in the formulation of the mixture are reported. The 5005 mixture was characterized by multiple investigation techniques, such as temperature dependence dielectric anisotropy, transmittance measurements image polarizing microscopy, and UV stability.

Numerical study of deformations induced by ac electric field in insulating flexoelectric nematic layers

2011 ◽  
Vol 19 (1) ◽  
Author(s):  
G. Derfel ◽  
M. Buczkowska
Keyword(s):  
Liquid Crystals ◽  
Electric Field ◽  
Time Dependence ◽  
Critical Frequency ◽  
Numerical Study ◽  
Dielectric Anisotropy ◽  
Low Frequencies ◽  
High Frequencies ◽  
Ac Electric Field ◽  
Time Period

AbstractThe influence of the frequency f of applied ac electric field on the time dependence of electric field induced deformations of homeotropic nematic layers is studied numerically. Three kinds of nematic liquid crystals were considered: non-flexoelectric nematic with negative dielectric anisotropy, Δɛ < 0dielectrically compensated nematic (Δɛ = 0) possessing flexoelectric properties determined by the positive sum of flexoelectric coefficients e = e11 + e33 > 0nematic characterised by both Δɛ < 0 and e > 0.It was found that at sufficiently low frequencies, the deformations varied with time. The deformations of purely dielectric nature had the period 1/(2f). When the frequency was increased, a stationary director distribution was achieved, determined by the rms value of the ac voltage. The time period of purely flexoelectric distortions was equal to 1/f. There was a well defined cut-off frequency above which these deformations vanished. In the case of dielectrically anisotropic and flexoelectric nematic, the flexoelectric contribution vanished above a critical frequency and the deformation of dielectric nature stabilized at high frequencies.

scholarly journals The Effect of Polar Substituents on Dielectric and Optical Transmittance Properties of two λ-shaped Mesogenic with Bromo and Chloro Substituents - A Comparative Study

1970 ◽  
Vol 8 (8) ◽  
pp. 59-65
Author(s):  
PB Chand ◽  
R Manohar
Keyword(s):  
Dielectric Properties ◽  
Functional Group ◽  
Optical Transmittance ◽  
Cole Plot ◽  
Frequency Range ◽  
Smectic A ◽  
Smectic C ◽  
Scientific World ◽  
Smectic A Phase ◽  
Polar Substituents

Dielectric properties of two λ-shaped mesogenic compounds 4-((2-bromo-4-nitrophenyl)diazenyl)-1,3-phenylene bis(4-(tetradecyloxy)benzoate) (14MV) and 4-((2-chloro-4-nitrophenyl)diazenl)-1,3-phenylene bis(4-(decyloxy)benzoate) (10-OCPNDE) have been studied as a function of temperature and frequency. The bromo substituents compound exhibits smectic C phase but chloro substituents compound smectic A phase. Our interest is to compare the macroscopic properties of the two compounds of same category but different functional group i.e Br or Cl. With this aim, the dielectric permittivity with temperature and frequency has been determined for both the compounds in planar alignment at frequency range 100Hz- 1MHz. In this paper, we reported the dielectric behaviour of the effect of bromo and chloro substituents on mesomorphic two λ-shaped mesogenic homologous series with bromo and chloro substituents. Key words: λ-shaped liquid crystals; Polar substituents; Dielectric properties; Cole-Cole plot. DOI: 10.3126/sw.v8i8.3851 Scientific World Vol.8(8) 2010 pp.59-65

A new theory of the nematic-smectic A-smectic C transition in liquid crystals

1987 ◽  
Vol 48 (8) ◽  
pp. 1241-1245 ◽  
Author(s):  
B.S. Andereck ◽  
B.R. Patton
Keyword(s):  
Liquid Crystals ◽  
Smectic A ◽  
Smectic C
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