Anisotropy of the dielectric constant of polyacetylene

The dielectric constant ? of polyacetylene films oriented by rolling was measured. The variation of ? and also that of the proton nuclear magnetic resonance line shape indicate that rolling partially isomerizes cis(CH)_x. For oriented trans(CH)_x we find ?_∥ = 5.7 and ?_? = 4.0 in the plane of the film. A calculation based on bond polarizabilities leads to qualitative agreement with experiment.     

On the dielectric constant of nonpolar fluids

Referring to a recent paper in this journal of Stell and Rushbrooke the deviation from the Clausius-Mossotti relation for the static dielectric constant of a nonpolar fluid is discussed. In particular a number of coefficients in the dielectric virial expansion have been evaluated for a hard-sphere system.     

On the dielectric constant of nonpolar fluids

We discuss the recent work of Wertheim on the dielectric constant of nonpolar fluids, and also present some new calculations on the Kirkwood-Yvon theory. These serve to emphasise the prime importance of the state dependence of the effective polarisability in interpreting deviations from the Clausius-Mossotti theory for real dense fluids.     

Some polymers of high dielectric constant

A class of highly conjugated macromolecules exhibiting extraordinarily high effective dielectric constants (DK = 50–900) is described. These polymers are of the polyacene radical quinone type, are highly purified, and exhibit electronic semiconduction. The dielectric constant varies only slightly with pressure (up to 20 Kbar), but strongly with frequency (300–300,000 cps) and moderately with temperature and field strength. The latter effect of field strength on the effective dielectric constant (and on the conductivity) required the development of special measurement techniques which are described. The unusual dielectric behavior can be accounted for assuming the presence of what amounts to a thermally generated plasma of electrons and holes, each locally mobile on extended regions of associated π-orbitals on the molecules. The postulated resulting “hyperelectronic” polarization of the locally mobile charges in external fields fits the observed high magnitude of the polarizability, as well as its field, frequency, and temperature dependence.     

Phthalocyanine with a giant dielectric constant

Compound 1 has been prepared by the reaction of 4-nitrophthalonitrile and trans-2-methoxy-4-(2-nitrovinil)phenol by the common method of nucleophilic substitution of an activated nitro group in an aromatic ring. The metallophthalocyanines 2, 3 were prepared by the reaction of a dinitrile derivative with Co(OAc)(2) or Zn(OAc)(2) in DMSO. The lutetium bis-(phthalocyaninato) complex 4 was obtained by treating the dinitrile derivative with lutetium acetate and DBU in 1-hexanol. The new compounds were characterized by elemental analyses, FT-IR, (1)H-NMR, MALDI-TOF MS and UV/Vis spectral data. The spectroscopic data of the new compounds were in accordance with the structures. The temperature and frequency dependence of dielectric and conduction properties of the spin coated film of compounds (2-4) have been studied by fabricating metal-Pc-metal structures. The results show that compound 2 has giant dielectric constant. At a low range of frequency and room temperature, ε' is found to be equal to 2.33 × 10(6), 1.53 × 10(4) and 1.03 × 10(4) for 2, 3 and 4, respectively. The giant dielectric behavior of 2 is mainly attributed to Maxwell-Wagner polarization. The obtained results also indicated that the frequency dependence of the dielectric permittivity, ε'(ω), exhibits non-Debye type relaxation for all temperatures investigated. The ac conductivity results gave a temperature dependent frequency exponent s. The results were compared with the prediction of the Quantum Mechanical Tunneling and Correlated Barrier Hopping models.     

The dielectric constant and oscillometric measurement

Summary New evidence is given that the characteristic conductance and susceptance curves of high frequency measurements, expressed as a function of the log of the electrolyte concentration, depend only on the physical parameters of the measuring cell, and the Debye effect plays only an insignificant role.

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Zusammenfassung Wie neuerlich gezeigt wurde, sind die Konduktanz- und Susceptibilitäts. kurven bei Hochfrequenzmessungen, ausgedrückt als Funktion des Logarithmus der Elektrolytkonzentration nur von den physikalischen Parametern der Meßzelle abhängig. Der Debye-Effekt spielt keine signifikante Rolle.

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Résumé On donne une nouvelle preuve que les courbes caractéristiques de la conductance et de la susceptance des mesures en haute fréquence, exprimées en fonction du log de la concentration de l'électrolyte, ne dépendent que des paramètres physiques de la cellule de mesure, et que l'effet Debye ne joue qu'un rôle minime.

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Presented at the Symposium on Analytical Chemistry, Graz, 29th September–1st October 1965.     

The dielectric constant of lamellar semicrystalline polymers

The problem of representing the dielectric constant of semicrystalline polymers in terms of the dielectric constants and volume fractions of the constitutent crystalline and amorphous phases is considered. For locally lamellar morphology, bounds based on uniform electric and displacement fields are derived. The equations also include the degree of crystal orientation as a parameter. For unoriented polymers the bounds are considerably tighter than the Hashin–Shtrikman bounds, the latter being the best possible without knowledge of phase geometries. The bounds presented here are sufficiently tight to represent the dielectric constant with practical accuracy for a number of examples of semicrystalline polymers. A treatment is also given of the dielectric constant where the lamellar morphology is further specified as being organized into spherulite-like structures. These bounds are somewhat tighter than the lamellar bounds.     

Nearly constant dielectric loss behavior in ionomers

The electrical conductivity of a series of ionomers has been characterized by measuring the electrical conductivity in a relatively broad range of frequencies and temperatures. At low frequencies, the conductivity of the ionomers exhibits a universal Jonscher power law (JPL), and at higher frequencies a nearly constant loss (NCL) behavior. The NCL for the ionomers is qualitatively similar to that observed for other inorganic ionic conductors. However, the magnitude of NCL for ionomers is lower than that observed for inorganic ionic conductors. The analysis of the conductivity master curves suggests that the conduction mechanism, which includes both the NCL and the JPL behaviors, is governed by ion hopping of the mobile ions.     

Low dielectric constant polyimide nanomats by electrospinning

The proper combination of material (i.e. fluorinated polyimides) and processing technique (electrospinning) could lead to the formation of polyimides with low dielectric constant, high thermo‐oxidative stability and glass transition temperature, and high hydrophobicity. The polyimides in this work were based on 4, 4‐bis [3′‐trifluoromethyl‐4′ (4′‐amino benzoxy) benzyl] biphenyl (Q) and various fluorinated and non‐fluorinated dianhydrides namely benzene‐1,2,4,5‐tetracarboxylic dianhydride, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride, and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA). Processing of the polyimides was carried out in poly(amic acid) stage by two different methods—electrospinning and solution casting for comparison purposes. The processing of polyimides by electrospinning led to enhancement in mechanical properties (dianhydride‐structure dependent) and hydrophobicity without sacrificing thermo‐oxidative stability and glass transition temperatures significantly. Also, low dielectric constants (as low as 1.43) could be attained by suitable combination of dianhydride (6FDA) with 4, 4‐bis [3′‐trifluoromethyl‐4′ (4′‐amino benzoxy) benzyl] biphenyl diamine. Copyright © 2011 John Wiley & Sons, Ltd.     

Re-interpretation of the solvent dielectric constant in coordination chemical terms

It is found for common aprotic solvents that the logarithm of the dielectric constants can be represented by a linear combination of the acceptor numbers (AN) and the donor numbers (DN) (or equivalent parameters), $$log \in = c_1 ({\rm A}{\rm N}){\text{ }} + {\text{ }}c_2 (DN){\text{ }} + {\text{ }}c_3 $$ With this equation, concepts of specific and non-specific solvation are brought under the umbrella of one treatment. The equation does not hold for the highly structured solvents. For these, the dielectric constants predicted on the basis of the acceptor and donor numbers are orders of magnitude larger than the experimental values, revealing how poorly the associates are dissociated by the macroscopically attainable electric fields.     

Computer simulation and the dielectric constant of polarizable polar systems

A theory presented recently, allowing the static and frequency-dependent dielectric constant of polar systems to be calculated in computer simulations with arbitrary boundary conditions, is extended to the polarizable case. For modified dipolar interactions not explicitly depending upon time, the resulting equations are found to be of the generalized Fröhlich-Glarum type.     

An interlayer model for the complex dielectric constant of composites

The complex dielectric constant of a composite with an interlayer was studied as a function of the volume fractions and the properties of the filler, the interlayer, and the matrix. The theoretical approach is analogous to the calculation of the shear modulus, the bulk modulus, and the termal expansivity of particulate filled polymers using the interlayer model (IM).An analytical expression describing the influence of an interlayer on the generalized dielectric constant of the composite as a function of the volume fraction and interlayer properties is derived.In the case of a composite with non-conductive constituents, the equations for static and oscillatory electric fields are similar. When conductive constituents are present, the complex dielectric constants have to be replaced by the generalized complex dielectric constants.For a composite of non-conductive materials, without interlayer, the obtained relation reduces to the classical Rayleigh equation. In the case of a composite with conductive constituents, also without interlayer, the complete solution of Wagner's theory is found. Special attention has been paid to the case of a water interlayer in a glass-bead filled non-conductive matrix material.     

Implications of a high dielectric constant in proteins

Solvation of protein surface charges plays an important role for the protonation states of titratable surface groups and is routinely incorporated in low dielectric protein models using surface accessible areas. For many-body protein simulations, however, such dielectric boundary methods are rarely tractable and a greater level of simplification is desirable. In this work, we scrutinize how charges on a high dielectric surface are affected by the nonpolar interior core of the protein. A simple dielectric model, which models the interior as a low dielectric sphere, combined with Monte Carlo simulations, shows that for small, hydrophilic proteins the effect of the low dielectric interior is largely negligible and that the protein (and solution) can be approximated with a uniform high dielectric constant equal to that of the solvent. This is verified by estimates of titration curves and acidity constants for four different proteins (BPTI, calbindin D(9k), ribonuclease A, and turkey ovomucoid third domain) that all correlate well with experimental data. Furthermore, the high dielectric approximation follows as a natural consequence of the multipole expansion of the potential due to embedded protein charges in the presence of the low dielectric core region.     

The dielectric constant of water: influence of the quadrupole moment

We examine the suggestion that the very high dielectric constant of water is associated with the absence of a significant component of the quadrupole tensor along the direction of the dipole moment. We find that although ?_zz ≈ 0, there is a large “effective axial” moment ?^eff_zz.     

On the theoretical calculation of the dielectric constant of dilute electrolyte solutions

In dilute ionic solutions, the solute-dependent dielectric constant varies as a linear function of concentration. In this note we consider alternative theoretical routes to the limiting slope, and compare numerical results for ions in dipolar hard-sphere and water-like solvents.