Dielectric-constant data

Plots showing the variation of the rate constant for the reaction between NICjHsh and C H5I in several solvents with different dielectric constants. Data from Table 9-2. 

Suresh, S J. and Naik, V.M. 2000. Hydrogen bond thermodynamic properties of water from dielectric constant data. J. Chem. Phys. 113, 9727-9732. 

Fio. 16. Dependence of solvent properties pertinent to RPC on composition of water-methanol mixture at 25 C. SuifisiM tension y data were obtained from Hmmemums (/i ) the viscosity and dielectric constant data c were taken from Carr and Riddick (135) and Akeriof (136), respectively. Reprinted from Horvdth and Melander (/29). J. Chroma-togr. Sci., with permission from Reston Publications. 

Fio. 20. Dependence of Mdvent propeitiet pertinent to RPC m composition of water-ethanol niixturet at 25 C. Surfhce tension y data were obtained from Timmermans (IS4) the viscosity and dielectric constant data were taken ftoni Saloeanu (/40) and Akeriof(/itf). 

At a quantitative level, near criticality the FL theory overestimates dissociation largely, and WS theory deviates even more. The same is true for all versions of the PMSA. In WS theory the high ionicity is a consequence of the increase of the dielectric constant induced by dipolar pairs. The direct DD contribution of the free energy favors pair formation [221]. One can expect that an account for neutral (2,2) quadruples, as predicted by the MC studies, will improve the performance of DH-based theories, because the coupled mass action equilibria reduce dissociation. Moreover, quadrupolar ionic clusters yield no direct contribution to the dielectric constant, so that the increase of and the diminution of the association constant becomes less pronounced than estimated from the WS approach. Such an effect is suggested from dielectric constant data for electrolyte solutions at low T [138, 139], but these arguments may be subject to debate [215]. We note that according to all evidence from theory and MC simulations, charged triple ions [260], often assumed to explain conductance minima, do not seem to play a major role in the ion distribution. 

Through a series of parametrization, the most suitable linear combination was (1/c — 1/c") where c = c + (c — corg), = 2c — c0rg, = bulk dielectric constant of the mixed solvent, corg = bulk dielectric constant of the pure organic component, and c = bulk dielectric constant of water. (The dielectric constant data were obtained from literature these references are not being cited in order to save space. Some of the c values were obtained by these authors by interpolation. For the convenience of the reader we have compiled the values of bulk... 

Dipole moments may also be derived by a consideration of the dielectric constant data themselves. Since amino acids and proteins are soluble only in polar solvents, the treatment which is applicable to dilute solutions of polar molecules in a non-polar medium cannot be applied here. However, the general theory of polar liquids developed by Onsager (S7) and Kirkwood (67) [see also Kirkwood in Cohn and Edsall [16), Chapter 12], is applicable here. According to Kirkwood s treatment, the dipole moment (/z) of an individual molecule in the liquid is in general different from its moment in the gaseous state because the attractions... 

All values taken at 20°C. Column labels log P refers to the logarithm of the octanol-water partition coefficient, log S / to the logarithm of the water solubility, mol , e to the solvent dielectric constant. Data from References 173 through 179. 

The "group" dipole moment of the amide functional group is calculated from dielectric constant data and found to be 2.0 Debyes in dry polymer films and 2.1 Debyes in films conditioned at 40% RH. The small increase in "wet" films is consistent with the water absorption data indicating that the effective water dipole moment decreases in the presence of amide groups. 

The data reproducibility was excellent as long as a single batch of control resin was used for the studies so that variables such as monomer purity and polymer molecular weight were controlled. In addition films were cast in a clean room to minimize dust incorporation which can result in large errors in film thickness measurements. Figure 3 shows the typical example and the worst case for dielectric constant data variability on these films. 

The conductivity of liquid sulfur has been measured by Feher and Lutz (J), Gordon (2), and Watanabe and Tamaki (3). Also Poulis and Massen (4) have calculated conductivity values for sulfur at 231° and 360°C from the dielectric-constant data of Curtis (5). The conductivities reported by Feher and Lutz are much lower than those of Watanabe and Tamaki, but the former data were obtained at lower temperatures than... 

N-methylpropionamide (NMP) has a liquid range of —30.9 to 148°C and a dielectric constant of 176 at 25°C. It has been much less studied than NMA, DMA, etc. Hoover has presented density and dielectric constant data of NMP-H2O at 20 to 40°C, and discussed the effects of these two highly structured solvents on each other. 

Dielectric constant data are abstracted from the compilation of solvent properties in J. A. Riddick and W. B. Bunger (eds.), Organic Solvents, Vol. II of Techniques of Organic Chemistry, TTiird Edition, Wiley-Interscience, New York, 1970. 

Dielectric constant data have been reported on several unreinforced polymers, including polyimides [19-21], silicones [22], epoxy resins [23], polyurethanes [23], polyaniline nanofibers [16, 17], zirconium nanocomposites [24], cross-linked polyethylene [15], low-density polyethylene [22], doped polyimines [19], polyimide-3-zirconium propoxide nanocomposites [24], poly linu-naphthyl ether [30], and cross-linked polyethylene-polyethylene polyacrylate acid blends [15]. 

C2ilculate dielectric constants within the fitted temperature range but should not be used for extrapolation outside this range. The user who needs dielectric constant data with more accuracy than can be provided by this equation is referred to Reference 1, which gives the original data together with their literature source. 

The dielectric constant, on the other hand, is not affected by ionic impurities in the polymer-solvent system and drops off in magnitude above the primary glass transition process. Figure 5b shows the dielectric constant profiles for the same SAN/acetone system discussed above. Van Tumhout et al. have shown that plotting the first derivative of the dielectric constant with respect to temperature is a very good way to delineate subtle T>Tg shoulder processes in dielectric constant data. 

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