Measurement of Dielectric Constant

For each pol5mier in this series, dielectric permittivity of polyimide films was measured by using Alpha High Resolution Dielectric Analyzer from Novocontrol-Germany, in the domain of frequencies from KT to 10 Hz, and it was approximated at the frequency equal to zero to obtain the value of dielectric constant (e ). 

5 METHOD OF TREATMENT WITH SUPERCRITICAL CARBON DIOXIDE (SC-CO  

The following experimental technique was applied The polymer film was weighed and placed into the cell. The films had the form of a disk with 15 mm diameter and thickness in the range from several to tens of microns. The cell was purged with CO2 to remove the air and water vapors, and it was sealed. Then it was heated to the temperatures shown in this chapter, the pressure was increased to the values also shown in this chapter, and it was kept a certain time necessary 

FIGURE 3.4 The curve of desorption of CO from polymer film after the swelling 

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Values of the mean-square dipole moment of PNA are determined from measurements of dielectric constants and refractive indices of the polymer in benzene. The dipole moment ratio and the temperature coefficient of both the dipole moment and the unperturbed dimensions are critically interpreted using the RIS model. Good agreement between theory and experiment is obtained by assuming that the gauche states about C(CH3)2— CH2 bonds have an energy 2.5 kJ mol-1 lower than the alternative trans states. 

The gas recommended is hydrogen chloride, HCI, because it has a large permanent dipole moment and because it has a boiling point low enough (-83.7°C) to permit measurements of dielectric constant to be made down to Dry Ice temperature (-78.5°C) if the option of measuring the dielectric constant at more than one temperature is chosen. 

Measurements of dielectric constants of solutions allow the deduction of not only how many waters are taken up and held irrotationally by ions, but also how the ions affect the frequency of the movements of molecules near them. This will help a person interested in electrostatic effects calculate the local pressure near an ion (Section 2.22.1). 

Measurements of dielectric constant as a function of frequency. These dielectric dispersion measurements permit the estimation of the relaxation times or rotary diffusion constants which characterize the rotary Brownian movement of the protein molecule. 

Dielectric measurements on thin films were made using a two-fluid cell technique as per ASTM D 150. The advantage of the two-fluid cell is that measurement of dielectric constant is independent of sample thickness, electrode spacing, and electrode area. Thin films can be stacked to increase testing accuracy. The reproducibility of the dielectric constant measurement using the two-fluid cell was 2%. 

Many substances cannot be obtained in the vapor state at sufficient pressures to make measurements of dielectric constant possible. To overcome this difficulty a large number of dielectric constant measurements of solutions have been carried out. As solvents substances such as benzene, dioxane or hexane which possess no electric moments, were usually chosen. For binary solutions equation (22) may be given the form... 

Measurements of dielectric constant in the 2-methyl-2-propanol-water system by Brown and Ives 1) are explicable in terms of a water-centered... 

The fundamental measurements of dielectric constant and resistivity in multiphase systems follow directly from methods used for solid systems (Curtis, 1915). The material resistivity (or electrical conductivity) together with the permittivity are useful parameters for calculating the charge relaxation time of the material. 

Dipole moments Measurement of dielectric constant Particularly useful for small molecules... 

Power Factor and Permittivity Measurements of dielectric constant and loss in polymeric solids and melts over a wide frequency range was described in detail elsewhere [Porter and Boyd, 1972]. 

Experimental dipole moments can be obtained in several different ways. The first and most widely used approach is based on the measurement of dielectric constants. The second group of methods utilizes microwave spectroscopy and molecular beams (the Stark effect method, the molecular beam method, the electric resonance method, Raman spectroscopy, etc.). 

Many dipole moments available in the literature were obtained from the measurements of dielectric constants in the vapor phase or in diluted solutions of polar compounds in nonpolar solvents [24-31]. All these methods are based on Debye s statistical theory [35]. 

The dielectric constants needed for the determination of dipole moments are obtained by a heterodyne beat method or the resonance and bridge methods. The instrument specifically adapted for measurements of dielectric constants for dipole moments is a dipole meter model DM-01 manufactured by Wissenschaflich-Technische Werkstatten, Weilheim, Germany, equipped with two different thermostatted cells for two ranges of dielectric constants (cell DFL-1, e 1.0 to 3.4, cell DFL-2, e 2 0 to 6.9). The other dipole meter which used to be available from Toshniwal Brothers, Ltd., Madras, India, is not sufficiently sensitive for measurements of dielectric constants of diluted solutions and is better suited for measurements of large differences, such as the dielectric constants and dipole moments of different solvents. 

K. Bergstrdm, Measurements of Dielectric Constants and Electric Dipole Moments in the Gas Phase, Lund Institute of Technology, Lund, 1973. 

Figure 2.4-8 Apparatus for measurement of dielectric constants and conductivities for C02-water and water-C02 emulsions.

To determine the electric dipole moment of a solute molecule from measurements of dielectric constant and refractive index. 

In practice, the elaborate measurements of dielectric constants of gases at different temperatures are usually circumvented, on the one hand by the use of dilute solutions and the application of additive relations for solvent and solute, and, on the other hand, by the theoretical calculation of a from the refractive index, so that /x can be found from measurements at one temperature only. 

Dipole moment, molecular n. It is found from measurements of dielectric constant (i.e., by its temperature dependence, as in the Debye equation for total polarization) that certain molecules have permanent dipole moments. These moments are associated with transfer of charge within the molecule, and provide valuable information as to the molecular structure. 

This technique is used principally for the rheological characterisation of polymers (Sections 18.1.3 and 18.1.4) and measurement of dielectric constant (Section 18.2). In the field of thermal and mechanical stability it has also found application in the fields of resin cure kinetics and resin cure monitoring. 

Electrochemical Sensors for Monitoring Conditions of Lubricants, Fig. 4 Interleaved parallel plate capacitor for measurement of dielectric constant and lubricating oil viscosity versus dielectric constant [22]... 

Riande et al. (21,22) synthesized the cis and tmns isomers of PCDS as well as the trans isomer of poly(l,4-cyclohexylenedimethylene adipate) (PCDA), and studied their polarity by measurements of dielectric constants and dipole moments. They observed that the trans isomer exhibited lower polarity than the cis one, and that the dipole moment decreased with the number of methylene groups of the diacid unit. The configurational properties of the two PCDS isomers were comparatively examined, both experimentally and theoretically, using the rotational isomeric state model. 

Kumar A., Sharma, S. (2007). Measurement of dielectric constant and loss factor of the dielectric material at microwave frequencies. Progress In Electromagnetics Research,... 

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