Ferroelectricity of Chiral Compounds in Highly Ordered Smectic Phases

1989 ◽  
Vol 173 ◽  
Author(s):  
Stanisław Wróbel ◽  
Matthias Pfeiffer ◽  
Ashók M. Biradar ◽  
Wolfgang Haase
Keyword(s):  
Relaxation Time ◽  
Molecular Motion ◽  
Bias Field ◽  
Goldstone Mode ◽  
Electric Permittivity ◽  
Frequency Range ◽  
Chiral Compounds ◽  
Chiral Phases ◽  
Smectic Phases

ABSTRACTMeasurements of the complex electric permitttivity for the Sm C* and for three highly ordered smectic phases: Sm I*, Sm J* and Sm K* of 4- (2 - methylbutyl)-phenyl-4′-(octyloxy)-(1,1′)-biphenyl-4-carboxylate (8 OSI) have been done in the frequency range from 5 Hz to 13 MHz. For the first three chiral phases the Goldstone mode was found with temperature independent critical frequencies, νc = 1.5kHz and the relaxation time τG = 106 μs - for the Sm C* phase, and νc = 1 kHz and τG - 160 μs - for the Sm I* one. In two highly ordered smectics, i.e. Sm J* and Sm K* with inter-layer correlations, the Goldstone mode seems to be suppressed. By applying a D.C. bias field of 1.4 kV/cm the Goldstone mode has been suppressed and shifted towards higher frequencies in both the Sm C* and Sm I* phase. For the Sm J* phase the Goldstone mode is very weak and practically insensitive to the bias field used. In the Sm K* phase there is no Goldstone mode like relaxation, and the only contribution to electric permittivity comes from the fast molecular motion connected with reorientation of molecules about their long axis.

scholarly journals Low Frequency Characteristics of TiO2(Rutile)–Glass Thick Films

1977 ◽  
Vol 4 (1) ◽  
pp. 1-7 ◽  
Author(s):  
B. Licznerski ◽  
K. Nitsch ◽  
B. Rzasa
Keyword(s):  
Relaxation Time ◽  
Dielectric Relaxation ◽  
Low Frequency ◽  
Frequency Characteristics ◽  
Electric Permittivity ◽  
Frequency Range ◽  
Ambient Conditions ◽  
Amorphous Glass ◽  
Tio2 Rutile ◽  
Normal Ambient

An analysis is made of the low-frequency characteristics of the permittivityε′and of tanδof a thick-film insulator containing rutile grains bonded with an amorphous glass. The appearance of dielectric relaxation associated with a maximum of tanδ, as well as characteristic Debye dispersions of the electric permittivity is observed. The relaxation time does not depend on the rutile concentration in the dielectric. An equivalent circuit describing the behaviour of a capacitor with such an insulator in the low frequency range is suggested. The experimental results are shown to be consistent with an analysis based on the assumption that a titanium ion relaxation process occurs in the rutile grains. In normal ambient conditions the influence of this kind of polarization disappears at frequencies higher than 102Hz;ε′and tanδthen change insignificantly and the value of tanδis conditioned by the hopping mechanism of conductivity in the glass and in rutile.

Hypersonic Velocity, Absorption and Relaxation in Molten CSNO3

1977 ◽  
Vol 32 (1) ◽  
pp. 57-60 ◽  
Author(s):  
H. E. Gunilla Knape ◽  
Lena M. Torell
Keyword(s):  
Relaxation Time ◽  
High Frequency ◽  
Viscosity Coefficient ◽  
Sound Waves ◽  
Frequency Range ◽  
Ultrasonic Velocities ◽  
Hypersonic Velocity ◽  
Frequency Shifts ◽  
Bulk Viscosity Coefficient ◽  
Good Agreement

Abstract Brillouin spectra of molten CSNO3 were investigated for scattering angles between 40 and 140° and in a temperature interval of 420-520 °C. An Ar+ singlemode laser was used for excitation and the total instrumental width was ~265 MHz. The measured frequency shifts and linewidths of the Brillouin components were used to determine velocities and attenuations of thermal sound waves in the frequency range 2.3-7.0 GHz. A dispersion of 4-5% was found between the present hyper­ sonic velocities and reported ultrasonic velocities. A considerable decrease in attenuation with frequency was observed in the investigated frequency range, with the value at high frequency ap­ proaching the classical attenuation. The results are in good agreement with Mountain's theory of a single relaxation time. The relaxation time of the bulk viscosity coefficient was calculated to 1.2×10-10S.

scholarly journals Operational Amplifiers Revisited for Low Field Magnetic Resonance Relaxation Time Measurement Electronics

Proceedings ◽  
2019 ◽  
Vol 42 (1) ◽  
pp. 1
Author(s):  
Najlaa K. Almazrouei ◽  
Michael I. Newton ◽  
Robert H. Morris
Keyword(s):  
Relaxation Time ◽  
Magnetic Resonance ◽  
Field Measurements ◽  
Time Measurement ◽  
Operational Amplifiers ◽  
Frequency Range ◽  
Sensor Applications ◽  
Low Field ◽  
Front End ◽  
Resonance Relaxation

Advances in permanent magnet technology has seen more reports of sensor applications of low field magnetic resonance. Whilst most are either in the 10–20 MHz range or in the earth’s field, measurements at below 1 MHz are beginning to become more widespread. This range is below the need for careful radio frequency electronics design but above the audio domain and represents an interesting cross over. Many commercial spectrometers do not include the pulse power amplifier, duplexer and preamplifier as these depend on the frequency range used. In this work we demonstrate that, with the current specifications of the humble operational amplifier, the most simple form of an inverting design using only two resistors and decoupling, can effectively provide this ‘front end’ electronics. The low powers used mean crossed Ge diodes provide an excellent duplexer and it is suitable for battery powered applications.

Relaxation time spectra from short frequency range small-angle dynamic rheometry

2014 ◽  
Vol 53 (5-6) ◽  
pp. 385-399 ◽  
Author(s):  
Oscar Vernáez ◽  
Alejandro J. Müller
Keyword(s):  
Relaxation Time ◽  
Small Angle ◽  
Frequency Range ◽  
Dynamic Rheometry

35Cl NQR and Molecular Motion in Solid C6X5Cl (X = H, F)

1992 ◽  
Vol 47 (1-2) ◽  
pp. 330-332 ◽  
Author(s):  
A. D. Gordeev ◽  
G. B. Soifer ◽  
A. P. Zhukov
Keyword(s):  
Relaxation Time ◽  
Molecular Motion ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Activation Energies ◽  
Spin Lattice Relaxation ◽  
Melting Points ◽  
Spin Lattice Relaxation Time ◽  
Spin Lattice ◽  
35Cl Nqr

AbstractThe 35Cl NQR frequency and spin-lattice relaxation time of solid chlorobenzene and chloropentafluorobenzene at temperatures from 77 K to the melting points have been measured and explained by thermoactivated librations and reorientations of the molecules around the normal to their plane. The activation energies of these motions have been estimated

Dielectric relaxation behaviour of liquid crystals with opposite orientation of -COO ester group in molecular core

2008 ◽  
Vol 16 (3) ◽  
Author(s):  
J. Rutkowska ◽  
P. Perkowski ◽  
W. Piecek ◽  
Z. Raszewski ◽  
J. Kędzierski
Keyword(s):  
Dielectric Relaxation ◽  
Dielectric Strength ◽  
Ester Group ◽  
Relaxation Processes ◽  
Goldstone Mode ◽  
Smectic Phases ◽  
Molecular Core ◽  
Temperature Dependences ◽  
The Stability ◽  
Experimental Values

AbstractDielectric measurements were performed for two smectogens, being structurally analogous with the opposite space orientation of the-COO ester group in the molecular core, using a HP4192A impedance analyser. Gold coated electrode cells of different thicknesses were used. Temperature dependences of the relaxation frequency fR and the inverse of the dielectric strength Δε′┴ −1 obtained by fitting experimental values of perpendicular components, i.e., the real ε′┴ and the imaginary ε″┴ parts of the complex dielectric permittivity to the Cole-Cole equation as well as the investigation of modification of relaxation processes under bias were determined for the SmC*, SmA*, and N* phases of studied compounds. One can conclude, on the basis of the above results, that dielectric relaxation processes observed by us in the studied compounds are similar to those of the soft and Goldstone mode typically observed by others in the SmC*, SmA*, and N* phases. It is concluded from acomparison of their properties with other related compounds that the link between the biphenyl moiety and-COO ester group is closely related to the stability of smectic phases.

BEHAVIOR IN ELECTRIC FIELDS OF SIMPLE BIOLOGICAL MEMBRANES

2001 ◽  
Vol 15 (09n10) ◽  
pp. 299-308
Author(s):  
MARIA HONCIUC ◽  
ELENA SLAVNICU
Keyword(s):  
Fatty Acids ◽  
Relaxation Time ◽  
Fatty Acid ◽  
Liquid Crystals ◽  
Theoretical Model ◽  
Electric Fields ◽  
Biological Membranes ◽  
Biological Processes ◽  
Electric Permittivity ◽  
Order Of Magnitude

The latest studies in biophysics and biochemistry have revealed the major role that liquid crystals (LC) and related phenomena play in biological processes. To account for a number of membrane mechanisms in view of the theoretical model developed by S. J. Singer, studies were carried out on mixtures of fatty acids (arachidic, lauric, butyric) and cholesterol in different weight percentages. Such mixtures may help one understand some mechanisms on which the operation of biological membranes relies. To this end, the way these mixtures behave in an electric field was studied. Electric measurements were conducted from which the average time of electric relaxation (τ) and average electric permittivity (ε r ) were determined. Depending on cholesterol percentage, changes by more than one order of magnitude were found to occur in the electric relaxation time. The ratio between the various fatty acid components did not influence the average time τ in any significant manner. By contrast, the relative electric permittivity ε r was seen to decrease by at least one order of magnitude with raising the cholesterol percentage. The electric properties of such systems essentially depend on changing the amount of cholesterol in the system.

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