Dielectric properties, estimation

There are a number of properties of molecules that are additive to a reasonable approximation, i.e. the value of such a property of a given molecule is an approximate sum of the values of the properties of either the atoms or bonds present. It has been shown that the dielectric constant is related to some additive properties and it is thus possible to make some estimate of dielectric properties from consideration of molecular structure. 

If ion pairs but not free ions are formed, the extent of ion pair formation may be estimated from the dielectric properties of the solution. This method has been used in studying the effect of Lewis acids on alkyl halides.164... 

The Hamaker constant A can, in principle, be determined from the C6 coefficient characterizing the strength of the van der Waals interaction between two molecules in vacuum. In practice, however, the value for A is also influenced by the dielectric properties of the interstitial medium, as well as the roughness of the surface of the spheres. Reliable estimates from theory are therefore difficult to make, and unfortunately it also proves difficult to directly determine A from experiment. So, establishing a value for A remains the main difficulty in the numerical studies of the effect of cohesive forces, where the value for glass particles is assumed to be somewhere in the range of 10 21 joule. 

The ability to estimate accurately the dielectric properties of a polymer is of value in the development of new materials for use in the electronics industry. The purpose of this chapter is to report on calculations that estimate the dielectric constant of polymers that are sufficiently novel that their dielectric properties of... 

Non-destructive methods include holographic interferometry, resistance transducers, stress-sensitive covers, and other similar techniques. In practice, the following physical methods of non-destructive monitoring of residual stresses are commonly used X-ray diffraction, measurement of dielectric properties, and ultrasonic control. The main purpose of these methods is to monitor the structural transformations or distortions taking place as a result of residual stresses and local deformations. However, the application of methods such as X-ray diffraction to measure distortions in unit cel dimensions, ultrasonics to measure elastic wave propagation velocities, etc., all encounter numerous experimental problems. Therefore, in ordinary laboratory conditions only quantitative estimations of residual stresses can be obtained. 

The present evidence is thus that kinetic effects may account for half or more of permittivity decreases of ionic solutions and this may be an important factor in determing the amplitude of the Y dispersion in conducting biopolymer solutions and lead to revisions in estimated nature and amount of bound water. The effect may also have some bearing on dielectric properties of cell interiors and membranes if these have appreciable conductances. It would seem premature to attempt definitive answers to such questions until the relative importance of static and kinetic effects in presumably simpler ionic solutions has been better established experimentally in comparison with theory which treats them self-consistently. 

As mentioned in a previous section, the dielectric properties are largely affected by the structural characteristics of solid solution. Since the bond valence is a function of bond strength and bond length," the structural characteristics largely depend on bond valence. Therefore the dielectric properties could effectively be estimated by bond valence. Let s examine the effects of A-site and B-site bond valence on the microwave dielectric properties of lead-based complex perovskite compounds. 

The difference in reorganisation energy can be estimated from the static and optical dielectric properties of the Uquid and soUd-state (see Sutin and Marcus (1985) for Uquid state and eq. 2.17 for the solid-state ... 

For pure liquids, the Debye equation suggests that the molar polarization should be a linear function of the reciprocal temperature. Furthermore, one should be able to analyze relative permittivity data for a polar liquid like water as a function of temperature to obtain the dipole moment and polarizability from the slope and intercept, respectively. In fact, if one constructs such a plot using data for a polar solvent, one obtains results which are unreasonable on the basis of known values of p and ocp from gas phase measurements. The reason for the failure of the Debye model in liquids is the fact that it neglects the field due to dipoles in the immediate vicinity of a given molecule. However, it provides a reasonable description of the dielectric properties of dilute polar gases. In liquids, relatively strong forces, both electrostatic and chemical, determine the relative orientation of the molecules in the system, and lead to an error in the estimation of the orientational component of the molar polarization. 

Estimate the MSA parameters for DMSO using the dielectric properties given in table 4.2 and the molecular properties in table 4.3. 

Estimation of the discreteness-of-charge potential requires a detailed model of the interfacial region which gives its dielectric properties and the location of images in the conducting metal phase. According to the model developed by... 

Polyethylene has become one of the most widely used materials for electrical insulation due to its excellent dielectric properties and low cost. Original estimates of its probable lifetime using Arrhenius type extrapolation led to lifetime predictions of the order of forty years or more and yet a substantial number of failures in transmission and distribution cables have been observed at times under ten years. For 1977 failures on HMW URD cable totalled 1697 a failure rate of 3,08 per 100 miles while XLP cables were 0.53 per 100 miles and increasing (5). This work was undertaken to find out the role played by the polymer molecule under separate thermal and electrical stress. 

Because the specific volume of polymers increases at Tg in order to accommodate the increased segmental chain motion, Tg values may be estimated from plots of the change in specific volume with temperature. Other properties such as stiffness (modulus), refractive index, dielectric properties, gas permeability. X-ray adsorption, and heat capacity all change at Tg. Thus, Tg may be estimated by noting the change in any of these values such as the increase in gas permeability. 

A complication in the interpretation of the distance attenuation of the rates is that both the nuclear and electronic factors decrease with distance. (Inner-shell contributions to the reorganization barriers have been estimated as 0.03 eV and 0.17 eV for Fc and Ru complexes, respectively.) Thus interpretation of the electronic factor requires correction for Aout as a function of n or d. Liu and Newton have modeled Aout for the ferrocene (radius a = 0.34nm) SAM-electrode assembly in terms of three zones (aqueous phase 1 , SAM film 2 , electrode 3 ) of different dielectric properties (see Section 7.12.4.4, Equation (64)). The solvent barrier is considerable and very sensitive to film thickness (L) increasing from 0.75 eV to 0.86 eV when the thickness is increased from 0.5nm to 1.5 nm. For AG°da = 0, variation of Aout with distance contributes 1 nm to j3. The simplified expression... 

However, in most cases a limited miscibility (depending on Ni and k) (see Eq. 12.52) is observed leading to two phases enriched in mie compmient which can be described by a concentration Q. In principle the cmicepts developed in Sect. 12.4.2 can be employed to model the dielectric properties of each phase. In principle by analyzing the frequency position of the a-relaxati(Mi and its dielectric strength, the unknown concentration of each component can be estimated assuming appropriate mixing rules. In practical work this can be difficult. Of special interest is again the case where one component is dielectrically invisible as also discussed in Sect. 12.4.2. 

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