Dielectric-measurement parameters

The microwave spectrum of isothiazole shows that the molecule is planar, and enables rotational constants and NQR hyperfine coupling constants to be determined (67MI41700>. The total dipole moment was estimated to be 2.4 0.2D, which agrees with dielectric measurements. Asymmetry parameters and NQR coupling constants show small differences between the solid and gaseous states (79ZN(A)220>, and the principal dipole moment axis approximately bisects the S—N and C(4)—C(5) bonds. 

Omura et al. (117) investigated PCBL with m-cresol as solvent. This solvent was chosen because not only was it advantageous for dielectric measurements but also we had found (23) that the cooperativity parameter of the system PCBL-m-cresol was unusually small compared with those of other systems... 

Values of the dipole moment ratio of PNS are obtained from dielectric measurements. From thermoelastic experiments, performed on polymer networks, the temperature coefficient of the unperturbed dimensions is determined. Analysis of these results using the RIS model is performed leading to the parameters given above. 

The RIS model, coupled with the Flory matrix method, is applied to the calculation of the unperturbed mean-square end-to-end distance in polylcyclohexene sulphone) as a function of several parameters. The calculations are performed for atactic, isotactic and syndiotactic chains the tacticity arises from the two possible ways, D and L, in which the rings can be attached to the main chain, assuming that the C—C bonds are all in the trans conformation, as indicated by dielectric measurements. 

Dielectric measurements are insensitive to gelation. This important point is mainly based on experiments with epoxy-amine reactions for which the dielectric parameters are controlled by ionic conductivity. More experiments with other chemistries are needed to reach a more universal conclusion. 

A preliminary step to dielectric measurement by wave-transmission techniques is to relate the basic wave parameter, called the propagation factor, 7 of the material, to permittivity. In terms of the propagation factor the equations for the electric and magnetic fields of a plane wave travelling in the x-direction in a uniform, infinite material are ... 

By treating surface recombination as a hopping process in the image charge potential, Scott and Malliaras [140] have derived a very simple equation that describes the injected current as a function of electric field, temperature, and measurable parameters of the organic, namely the dielectric constant, the site density, and the drift mobility. The current has the usual form of thermionic emission, but with an effective Richardson constant that is several orders of magnitude lower than that in inorganic semiconductors. The results of the model are in... 

Nevertheless the use of dielectric materials obtained by conductive filler dispersion (carbon black, graphite fibres, metallic powders) is limited. As a matter of a fact material performances are dependent on the filler content as well as particle aggregation phenomena. These composites require a high level of reproducibility and their behaviour is linked to the control of electronic inter-particular transfer. The measured parameter (complex permittivity) depends on the texture of the percolation aggregates and consequently on the processing conditions. The percolation threshold (the particle concentration, after which particles are in contact and the electrical current exists) depends on the particle shape (sphere, plates or fibres). 

We present here dielectric measurements on emer-aldine salt samples at various doping levels for three different counter-anions, over a wide range of frequency (130 MHz-20 GHz). By changing the nature of the counter-anion, it is possible to vary the distance between neighbouring chains and we will show how the variation of this parameter will affect microwave properties. 

In continuation to our previous reported studies, the dielectric properties of the cellulose ether-transition metal complexes were examined [18]. The aim of this investigation was to find the relation between the dielectric measurements [permittivity and relaxation time] with the previous proposed structures, and ligand field parameters. The polymer complexes chosen for this study were prepared from cellulose ethers [CMC and HEC] with transition metals CuCl2, NiCl2, C0CI2 and FeCls. The dielectric properties were studied over a frequency range 0.1-80 kHz, at 25°C. Example of the relation between the permittivity [c ] and dielectric loss... 

On comparison of the dielectric measurements with the previously calculated nephlauxetic parameter[11-13], Tables 7.10 and 7.11 show a good relation between the increase in the metal content, which is considered to be a measure for complex formation, and degree of covalence of metal-ligand-o bonds Q8-value) of cellulose ether complexes with Ni(II), Co(II) and Fe(III) ions. We excluded the complexes with Cu(II), because the geometry structure proposed for these complexes square planner Cu(II) complexes could not be calculated the j8-value. The decrease in the value of fi indicates considerable overlap with a strong covalent metal. 

It would be important to understand in molecular terms the mechanisms underlying the difference in the various dielectric parameters that were measured. Parameters such as conductivity and permittivity reflect the distribution of free and bound charges, in membranes, respectively, and also the polarizability of various components. 

In the calculation of 0(f), the chain is assumed to have the type-A dipoles without inversion. In Equations (3.35) and (3.36), Tr,g and Xr, respectively, indicate the viscoelastic and dielectric relaxation times of the slowest Rouse mode. These Tr can be expressed in terms of the directly measurable parameters, the total friction of e chain (= NQ, and the mean-square end-to-end distance at equilibrium (R )j,q - Nb / as shown in Equation (3.36). Thus,... 

Although the success of the empirical solvent parameters has tended to downgrade the usefid-ness of the dielectric approach, there are correlations that have succeeded as exemphfied by Figure 13.1.1. It is commonly held that the empirical solvent parameters are superior to dielectric estimates because they are sensitive to short-range phenomena not captured in dielectric measurements. This statement may not be generahzed, however, since it depends strongly on the chemical reaction investigated and the choice of solvents. For instance, the rate of the Menschutkin reaction between tripropylamine and methyl iodide in select solvents correlates better with the log e function than with the solvent acceptor number. ... 

Measurement of spin-lattice enhancement in water and plasma solution An measured in 16 solvents. Plot of vs. dielectric constant parameter... 

The province of conventional dielectric measurements is here taken to be the determination of the relations of the polarization E and current density J. to the electric field in the macroscopic Maxwell equations. Proper theory should account for these relations in condensed phases as a function of state variables time dependence of applied fields and molecular parameters by appropriate statistical averaging over molecular displacements determined by the equations of motion in terms of molecular forces and fields. Simplifying assumptions and approximations are of course necessary. One kind often made and debated is use of an effective or mean local field at a molecule rather than the sum of microscopic... 

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