Dielectric measurement

Increasingly, dielectric measurements are being used to characterize the water content of emulsions. One model for the dielectric constant of a suspension, ... 

Transitions. Samples containing 50 mol % tetrafluoroethylene with ca 92% alternation were quenched in ice water or cooled slowly from the melt to minimise or maximize crystallinity, respectively (19). Internal motions were studied by dynamic mechanical and dielectric measurements, and by nuclear magnetic resonance. The dynamic mechanical behavior showed that the CC relaxation occurs at 110°C in the quenched sample in the slowly cooled sample it is shifted to 135°C. The P relaxation appears near —25°C. The y relaxation at — 120°C in the quenched sample is reduced in peak height in the slowly cooled sample and shifted to a slightly higher temperature. The CC and y relaxations reflect motions in the amorphous regions, whereas the P relaxation occurs in the crystalline regions. The y relaxation at — 120°C in dynamic mechanical measurements at 1 H2 appears at —35°C in dielectric measurements at 10 H2. The temperature of the CC relaxation varies from 145°C at 100 H2 to 170°C at 10 H2. In the mechanical measurement, it is 110°C. There is no evidence for relaxation in the dielectric data. 

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. 

Kabanov [351] has provided an excellent review of the application of measurements of electrophysical effects in studies of the thermal decomposition of solids, including surveys of electrical conductivity, photoconductivity, dielectric measurements and interface (contact), Hall and thermal (Seebeck) potentials. Care must be exercised in applying the results obtained in such studies to the interpretation of data for thermal decomposition in the absence of an applied electric field since many examples have been given [352] in which such a field markedly influences the course of decomposition. 

Dielectric measurements were used to evaluate the degrees of inter- and intramolecular hydrogen bonding in novolac resins.39 The frequency dependence of complex permittivity (s ) within a relaxation region can be described with a Havriliak and Negami function (HN function) ... 

Hence Rayleigh scattering gives the same information about non-polar molecules as dielectric measurements do on polar molecules. 

Dielectric enrichment, 23 109 Dielectric materials, polyimide, 20 278 in multilayer capacitors, 11 102 Dielectric measurements, 10 17, 425-426 Dielectric overlayers, in compound... 

For the dielectric loss measurement by a bridge (Ando Co. TR-10C),metal-PPE-metal sandwich specimens were prepared on the silicon dioxide substrate (Corning 7059). Evaporated aluminum was used as a metal electrode. The PPE film for the use of dielectric measurement was formed with the discharge electrode whose surface area was 26 cm2 and the remainder of the electrode was covered by the Teflon plate. Two kinds of samples were prepared for this experiment. One of them was formed at 5 KHz, 0.5 torr, 20 cm3STP/min and 5 watts. The other was formed at 13.56 MHz, 0.5 torr, 40 cm3STP/min and 25 watts. 

Fig. 4.10 a Characteristic relaxation times determined from dielectric measurements [137] (diamonds), and from NSE spectra at (triangles) for triol (open symbols) and PU (solid symbols). The full lines correspond to Vogel-Fulcher and the dotted lines to Arrhenius descriptions, b Relaxation times from NSE spectra have been arbitrarily multiplied by a factor 6 for triol and 40 for PU to build a normalized relaxation map. (Reprinted with permission from [127]. Copyright 2002 Elsevier)... 

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-... 

Data from mechanical and dielectric measurements can be related in a qualitative, if not quantitative, manner. Formally, the dielectric constant can be regarded as the equivalent of the mechanical compliance. This highlights the fact that the dynamic... 

The objective of the Springer KBES is twofold To ensure a high-quality part in the shortest autoclave curing cycle duration. This KBES is similar to QPA in that sensor outputs are combined with heuristics not with an analytical curing model. The rules for compaction dictate that dielectrically measured resin viscosity be held Constant during the First temperature hold in the autoclave curing run. The autoclave temperature is made to oscillate about the target hold temperature in an attempt to attain constant viscosity. Full pressure is applied from the cure cycle start. 

The most familiar method of evaluating is by dielectric dispersion experiments, in which the real and imaginary parts of the complex dielectric constant over those of the solvent are determined as functions of frequency. It is the value of referring to the state of vacuum that can be correlated with the molecular structure of the solute. Polymers cannot be dispersed in the gaseous state. Furthermore, solvents effective for polypeptides are usually polar, and only approximate theories are presently available for the estimate of vacuum < 2> from dielectric measurements with polar solvents. Therefore the dipolar information about polypeptides is always beset with ambiguity in absolute magnitude as well as in interpretation. 

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... 

Acknowledgments—The authors are grateful to the Boris Kidri6-Fund for some financial assistance and to Dr. D. Leskovsek and Mr. 3. Oman for the permission to use their instrument for the dielectric measurements. The spectroscopic work has been executed at the Boris Kidri6 Institute and the authors thank the Director, Dr. N. Samee, for the facilities pufc at their disposal. 

Samples of PVB are prepared, having an isotactic content of 46 %. Dielectric measurements are performed in solutions of both samples in dioxane and 1-methylnaphthalene at several temperatures, and dipole ratios Dx = lxm2 are found to be 0.52 and 0.45, respectively. No noticeable dependence of Dx with molecular weight is found the variation of Dx with temperature is too small to allow an accurate determination of Its temperature coefficient. An RIS model is derived and used to calculate dipole and characteristic (C = 0/o/2) ratios. 

Dielectric measurements are carried out on PPOA and PPODG. The dielectric spectrum of PPOA in the bulk presents a prominent glass-rubber relaxation followed by a subglass absorption. The low-molecular-weight compound only exhibits a prominent glass-liquid absorption followed by a diffuse and weak subglass relaxation. This behaviour cannot be explained in terms of only intramolecular interactions, and therefore intermolecular interactions must play an important role in this process. 

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. 

The dielectric measurements were carried out in a plate capacitor and frequency dependences of complex permittivity e = e — is (e and e" being its real and imaginary part, respectively) were determined [33] in the range /= 20 Hz- 200 kHz. 

Dielectric Measurements. Plasticizer efficiency can also be determined by measuring the electrical dissipation factor (damping) which is given by ... 

Table XI shows AT values obtained from dielectric measurements (34, 35, 36).

The behavior of plasticizers in a polymer has already been examined by Wiirstlin (16) with dielectric measurements. However, this method is not sensitive enough to detect the plasticizer behavior in the system at small plasticizer concentrations. Luther and Weisel (12) have also pointed out this fact as a result of their DC measurements of PVC-plasticizer systems. The following measurements deal with the behavior of plasticizers in polystyrene. 

G. R. Fleming In simple liquids such as methanol and ethanol there is no evidence for relaxation times slower than expected from dielectric measurements. Glasses at room temperature clearly show time scales that are infinite on our measurement time scale. In complex liquids such as glycerol-water mixtures and ethylene glycol, we may observe time scales that are longer than dielectric relaxation, but further studies are required to confirm this. 

Dielectric measurements in non-polar solutions of polymers having a unbalanced dipole moment along the chain therefore provide a simple method for obtaining t , . 

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