Difference dielectric measurements

Difference dielectric measurements were obtained by placing the unirradiated PNF spectra in the memory of the dielectric system, and subtracting the unirradiated spectra from the irradiated. 

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. 

As we have seen, the constant-force images depend on the local dielectric constant. We will now discuss the effect of the dielectric constant by calculating the relation between true and measured heights of a flat parallel film on a surface of different dielectric constant. 

Equations (7.6) and (7.7) provide a means of determining excited dipole moments together with dipole vector angles, but they are valid only if (i) the dipole moments in the FC and relaxed states are identical, (ii) the cavity radius remains unchanged upon excitation, (iii) the solvent shifts are measured in solvents of the same refractive index but of different dielectric constants. 

Static dielectric measurements [8] show that all crystals in the family exhibit a very large quantum effect of isotope replacement H D on the critical temperature. This effect can be exemphfied by the fact that Tc = 122 K in KDP and Tc = 229 K in KD2PO4 or DKDP. KDP exhibits a weak first-order phase transition, whereas the first-order character of phase transition in DKDP is more pronounced. The effect of isotope replacement is also observed for the saturated (near T = 0 K) spontaneous polarization, Pg, which has the value Ps = 5.0 xC cm in KDP and Ps = 6.2 xC cm in DKDP. As can be expected for a ferroelectric phase transition, a decrease in the temperature toward Tc in the PE phase causes a critical increase in longitudinal dielectric constant (along the c-axis) in KDP and DKDP. This increase follows the Curie-Weiss law. Sc = C/(T - Ti), and an isotope effect is observed not only for the Curie-Weiss temperature, Ti Tc, but also for the Curie constant C (C = 3000 K in KDP and C = 4000 K in DKDP). Isotope effects on the quantities Tc, P, and C were successfully explained within the proton-tunneling model as a consequence of different tunneling frequencies of H and D atoms. However, this model can hardly reproduce the Curie-Weiss law for Sc-... 

Here we link these different results and interpretations together by dielectric measurements on a series of synthetic faujasites with four differ-... 

The rate constant k t) for the monomer addition to the ion pair can be relatively easily determined in different ways by extrapolation of Equations 5a and 5b (Figure 5a, b), or by kinetic measurements of the polymerization where the dissociation of the ion pairs is completely suppressed by the addition of a large enough excess of Na+ ions. If the so-measured constants k t) are plotted according to Arrhenius equation, the pattern shown in Figure 9 is obtained for five solvents of different dielectric constants. 

IR spectra measurements as well as variation of the film thickness, shrinkage, and refractive index demonstrated substantial differences in the mechanisms of thermal decomposition of films prepared from the exclusively metal alkoxide precursor and from the metal alkoxides modified by 2-ethylhexanoic acid. These differences affect the evolution of film microstructure and thus determine the different dielectric properties of the obtained films. The dielectric permittivity of the films prepared from metal alkoxide solutions was relatively low (about 100) and showed weak dependence ofthe bias field. This fact may be explained by the early formation of metal-oxide network (mostly in the... 

Summarizing the information from the optical, electrooptical, and dielectric measurements we can draw several structures which are consistent with the crystallographic data but differ in the tilt and polarization distribution (Fig. 9). There is no direct method which would enable one to determine unambiguously which structure is correct, and we are left with some freedom for speculation. It seems... 

Dielectric measurements on PET [13], over a range of five different frequencies between 1 Hz and 10 kHz, at temperatures between - 120 and 80 °C, are shown in Figs. 12 and 13 for the dielectric constant, er> the loss tangent, tan <5, respectively. 

Polymer properties are very often dependent on the polymer preparation. So, a good monitoring of the polymerization process is the key step to obtaining good and reproducible materials. The extent of the polymerization can be controlled in different ways. IR is the most usual [27,30] but is not very accurate and requires the extraction of samples to analyze. Recently, an in situ monitoring of PMR-15 processing has been provided by means of frequency-dependent dielectric measurements [33,34]. This non-destructive technique allows the characterization of all the steps of the curing process and thus they can be optimized. 

Dielectric Measurements. The dielectric loss (c") curves at different frequencies for samples containing 100, 80, 40, and 0% PVC, respectively, are shown in Figures 4, 5, 6, and 7. Figure 8 is a composite of the dielectric loss data at 1 kHz for each sample. The general characteristics of a and p relaxation peaks of the component polymers and their mixtures parallel the results of dynamic mechanical measurements. For each... 

As mentioned previously, the complex dielectric permittivity (g>) can be measured by DS in the extremely broad frequency range 10-6-1012 Hz (see Fig. 1). However, no single technique can characterize materials over all frequencies. Each frequency band and loss regime requires a different method. In addition to the intrinsic properties of dielectrics, their aggregate state, and dielectric permittivity and losses, the extrinsic quantities of the measurement tools must be taken into account. In this respect, most dielectric measurement methods and sample cells fall into three broad classes [3,4,91] ... 

The dielectric relaxation properties in nano-PS with different thicknesses have been investigated recently over a wide range of frequency and temperature [160,161]. The dielectric properties of the PS samples were measured in the 20-Hz to 1-MHz frequency range and in the 173 to 493 K temperature interval. For all the dielectric measurements, the amplitude of a sinusoidal ac-voltage source was maintained 1 V so that the average electric field across our sample was of the order of hundreds of volts per centimeter depending on the sample thickness. It was verified that the response was linear with respect to the ac-voltage amplitude such that a linear response analysis could be utilized for our sample. 

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