Dielectric constants values

The dipole moments of the hydrogen halides decrease with increasing atomic number of the hydrogen, the largest difference occurring between HF and HCl, and association of molecules is not an important factor in the properties of FICl, HBr and HI. This change in dipole moment is reflected in the diminishing permittivity (dielectric constant) values from HF to HI. 

Typical dielectric constant values for taw materials are 2.6—3.0 for natural mbber iasulation, approximately 2.2 for polyethylene, and approximately... 

Numbered as in Table 8-2 and ranked in order of inereasing dielectric constant. "Values uncertain. 

Dielectric constant values are at 25° C unless stated otherwise. 

These YA values are found not to run in parallel with the dielectric constant values for the solvents concerned. Obviously the dielectric constant value for the solvent must be involved in some way in YA, as separation of opposite charges is a crucial feature of the rate-limiting step in an SN1 reaction formation of the T.S. leading to the ion-pair intermediate (47). But specific solvation of the separating charges must also be involved and YA will reflect those, and quite possibly other properties of the solvent as well. It is common to describe YA as representing a measure of the ionising power of the solvent A. 

Dielectric constant values listed in Tables V-VII permit safe use of the stepwise procedure for preparing mixed solutions without changing the... 

The dielectric constant of the pure cyanurate network under dry nitrogen atmosphere at 20 °C is 3.0 (at 1 MHz). For the macroporous cyanurate networks, the dielectric constant decreases with the porosity as shown in Fig. 57, where the solid and dotted lines represent experimental dielectric results together with the prediction of the dielectric constant from Maxwell-Garnett theory (MGT) [189]. The small discrepancies between experimental results and MGT might be due to the error in estimated porosities, which are calculated from the density of the matrix material and cyclohexane assuming that the entire amount of cyclohexane is involved in the phase separation. It is supposed that a small level of miscibility after phase separation would result in closer agreement of dielectric constants measured and predicted. Dielectric constant values as low as 2.5 are measured for macroporous cyanurates prepared with 20 wt % cyclohexane. 

Both the dielectric constant and dissipation factor are measured by comparison of results obtained with those obtained from a sample with known dissipation factor or dielectric constant values or substitution in an electrical bridge. 

Highly fluorinated molecules have a nonpolar character and an extremely low polarizability, inducing only weak intra- and intermolecular interactions. As a consequence, perfluorocarbons behave almost like ideal liquids they are very compressible and have very high vapor pressure. For example, the physical properties of perfluoro-hexane, heptafluorohexane, and hexane are reported in Table 1.2 The effect of the polar character of the hemifluorinated compound (heptafluorohexane) on the dielectric constant value is remarkable. 

Volume Resistivity and Dielectric Constant Values of Polymeric insulating Materials... 

Table 1.4 Solvent descriptors of organic solvents commonly used for biocatalysis. Sw/o (solubility of water in solvent, wt%) So/w (solubility of solvent in water, wt%) and e (dielectric constant) values from [78], log P (P = partition coefficient between octanol and water), ET (empirical polarity parameter by Reichardt-Dimroth) and HS (Hildebrand solubility parameter, )l, cm J, ) from [79].

Figure 12.1 shows how well the predicted results agree with the experimental values listed in Table 12.2. The predictions consistently overestimate experimental dielectric constant values for this series of samples. The difference varies from 12 to 27% of the experimental values. Qualitatively, predictions follow the same trend as experiment. The calculated slope for the best straight-line fit through the data points is equal to 0.822 with a standard deviation of 0.088. The correlation coefficient is equal to 0.881. For several of the polyimides tested here the method... 

Figure 12.2 shows the results of comparisons between prediction and experiment for the polyimides listed in Table 12.3. The correlation coefficient is determined to be 0.767. Its value can be improved to 0.957 by not considering the polyimide whose predicted dielectric constant value is equal to 3.02. The slope of the best-fit line is equal to 0.737, with a standard deviation of 0.232. 

However this would necessitate the determination of the derivative of a with respect to Z. This quantity cannot be measured with enough accuracy, especially when the association constant KA is small (this is the case in the high dielectric constant values of the solvents studied D 30). We have made two conductance runs, in a 59.02% water-THF mixture and in a 81.90% water-AC... 

The abnormally high dielectric-constant values observed for certain liquid substances, such as water and ammonia, were attributed by Latimer and Rodebush to continued polymerization through hydrogen-... 

An approximate value of the radius of the ionic atmosphere r as a function of concentration, for a uni-univalent (1-1) electrolyte at 25 °C and water as solvent, considering 79 as the dielectric constant value, may be obtained from the relationship... 

The dielectric constant values in Table 2.8 also suggest that, while hydrate water molecules reorient rapidly compared to molecules in other solids, reorientation rates are only one-half those in ice. The hydrate value is lower than that of ice due to the lower density of hydrogen-bonded water molecules. 

The dielectric constant of coal is strongly dependent on coal rank (van Krevelen, 1961 Speight, 1994, and reverences cited therein). For dry coals the minimum dielectric constant value is 3.5 and is observed at about 88% w/w carbon content in the bituminous coal range. The dielectric constant increases sharply and approaches 5.0 for both anthracite (92% carbon) and lignite (70% carbon). The Maxwell relation which equates the dielectric constant to the square of the refractive index for a polar insulators generally shows a large disparity even for strongly dried coal. 

Fig. 16. Electric field/concentration phase diagrams separating the homogeneous (acentric or ferroelectric) phase region from phase-separated regions for various values of host dielectric constant (curves 1 through 5 correspond respectively to dielectric constant values ol 2, 3, 5, 7, and 10). Field (e or ,) and concentration (x) are in dimensionless units as described in the text...

Solvation was also modeled, using a range of dielectric constant values 2, 4, and 80. The barriers for C5-protonation by methylammonium become increasingly larger as a higher s is used at s = 2, for example, the energy barrier to protonation increases to 26 kcal mol-1. The authors note, however, that these continuum models, which do not explicitly account for solvent or specific protein residues (see above), may not accurately represent the active site. 

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