Dielectric-experimental parameters Dispersion

We used the dielectric function e of bulk MgO calculated from oscillator parameters determined by Jasperse et al. (1966), together with the dielectric function em of the KBr matrix given by Stephens et al. (1953) (corrected by June, 1972), to calculate the absorption spectrum (12.37) of a dilute suspension of randomly oriented MgO cubes. These theoretical calculations are compared with measurements on well-dispersed MgO smoke in Fig. 12.16c. Superimposed on a more or less uniform background between about 400 and 700 cm-1, similar to the CDE spectrum, are two peaks near 500 and 530 cm- , the frequencies of the two strongest cube modes. It appears that for the first time these two modes have been resolved experimentally. If this is indeed so we conclude that the widths of individual cube modes are not much greater than the width of the dominant bulk absorption band. Genzel and Martin (1972)... 

The analysis of the experimental results by the theory of Kimura et al. give interesting clues for understanding the polypeptide liquid crystal. In Fig. 22 the parameters fi, which are related to the attractive dispersion force proposed by Maier and Saupe and can be obtained from the slopes in the 1/S vs. 1/T plots or the values of Tj, are plotted against the dielectric constants of solvents. B is... 

As illustrated in some of these figures, all the a-loss peaks are well-fitted by the one-sided Fourier transform of the KWW over the main part of the dispersion. Thus, the experimental fact of constant dispersion at constant xa can be restated as the invariance of the fractional exponent KWW (or the coupling parameter n) at constant xa. In other words, xa and (or n) are co-invariants of changing thermodynamic conditions (T and P). If w is the full width at half-maximum of the dielectric loss peak normalized to that of an ideal Debye loss peak, there is an approximate relation between w and n given by n= 1.047(1 — w-1) [112],... 

Photophysical and photochemical processes in polymer solids are extremely important in that they relate directly to the functions of photoresists and other molecular functional devices. These processes are influenced significantly by the molecular structure of the polymer matrix and its motion. As already discussed in Section 2.1.3, the reactivity of functional groups in polymer solids changes markedly at the glass transition temperature (Tg) of the matrix. Their reactivity is also affected by the / transition temperature, Tp, which corresponds to the relaxation of local motion modes of the main chain and by Ty, the temperature corresponding to the onset of side chain rotation. These transition temperatures can be detected also by other experimental techniques, such as dynamic viscoelasticity measurements, dielectric dispersion, and NMR spectroscopy. The values obtained depend on the frequency of the measurement. Since photochemical and photophysical parameters are measures of the motion of a polymer chain, they provide means to estimate experimentally the values of Tp and Tr. In homogeneous solids, reactions are related to the free volume distribution. This important theoretical parameter can be discussed on the basis of photophysical processes. 

By using suitable extrapolations [3] of the experimental data, beyond the upper and lower frequency limits of the measurements, and carrying out a Kramers-Kronig analysis, it is possible to obtain the dispersion of the real parts of the dielectric function and of the conductivity. The latter function is particularly suited for a comparison with the results of theoretical models, and for the determination of physical parameters by model fittings. 

However, ifp is of a negative value, then the yield stress will decrease as increases, which is unable to be explained by the polarization model but was experimentally observed, rhe parameter p only becomes positive when the dielectric loss tangent of the dispersed solid material is larger than 0.1, as we demonstrated before both experimentally and theoretically. Eq. (69) and (70) incorporates the dielectric criteria proposed earlier. Figure 13 shows the calculated yield stress using Eq.(69) as the function of the particle volume fraction at the particle-to-oil dielectric ratio 10, ds JdT =-2.4x 10 C experimentally determined for the silicone oil, and dc JdT -0,4 C as dc JdJ should be larger than zero for the ER... 

Fig. 11. Comparison of experimental dispersion data with those computed from model [12] - Illite-NaCl solution aggregate. Water content 159 % (weight water/dry weight of clay). Pore fluid aqueous NaCl solution, conductivity 10 crrr. Dielectric constant. Conductivity. Solid lines are calculated from optimized (bestfitting) model parameters.

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