Dielectric constant measurements

It has been shown that the polarizability of a substance containing no dipoles will indicate the strength o/any dispersive interactions that might take place with another molecule. In comparison, due to self-association or internal compensation that can take place with polar materials, the dipole moment determined from bulk dielectric constant measurements will often not give a true indication of the strength of any polar interaction that might take place with another molecule. An impression of a dipole-dipole interaction is depicted in Figure 11. 

The bulk properties of mixed solvents, especially of binary solvent mixtures of water and organic solvents, are often needed. Many dielectric constant measurements have been made on such binary mixtures. The surface tension of aqueous binary mixtures can be quantitatively related to composition. ... 

In order to prepare the samples for dielectric-constant measurements, etherdiacrylate 6 was mixed with a trace amount of AIBN at room temperature in a cylindrical donut mold made from General Electric RTV 11 silicon molding compound. The donuts had an outer diameter of 7.0mm, an inner diameter of 3.0 mm, and a thickness of 3.0 mm the semisolid triacrylate 3 was mixed with a... 

Table 11.1, Summary ofData for Dielectric Constant Measurements ... 

ACKNOWLEDGMENT We are indebted to Mr. Jones K. Lodge of SFA, Inc. for the dielectric constant measurements. Partial funding support from the Office of Naval Research is gratefully acknowledged. 

A resolution into two or more components always occurs if the solvent has a high proton affinity, so that a solvent molecule can form a particularly stable association with a phenol molecule as a result of an energetically favourable mutual orientation. This is the case, for example, if benzene and toluene are used as the solvents. However, this effect is even more pronounced in the case of cyclohexene. Dielectric constant measurements for phenol in various solvents agree with this observation. In particular, the dipole moments in benzene and cyclohexene (1-45 and 1-79 D respectively), are considerably greater than the value of 1-32 in cyclohexane. Liittke and Mecke (1949) attributed this effect to the ability of this unsaturated solvent to act as a proton acceptor, i.e. to form 7r-complexes. 

A vast amount of data based on dielectric constant measurements of substances in dilute solution in nonpolar solvents indicate that the theory is correct, but it looses validity and breaks down completely in the case of strongly polar media. It is interesting to notice that such a breakdown can be shown by the concept of the Curie point, introduced in connection with studies of magnetism but directly applicable to the case of dielectric constants. The dielectric constant can be related to the molar polarizability P and the molar concentration c by q. (21) and the value of P itself is given by Eq. (22). It is obvious that P increases as T dimin-... 

The dielectric constant of the pure cyanurate network under dry nitrogen atmosphere at 20 °C is 3.0 (at 1 MHz). For the macroporous cyanurate networks, the dielectric constant decreases with the porosity as shown in Fig. 57, where the solid and dotted lines represent experimental dielectric results together with the prediction of the dielectric constant from Maxwell-Garnett theory (MGT) [189]. The small discrepancies between experimental results and MGT might be due to the error in estimated porosities, which are calculated from the density of the matrix material and cyclohexane assuming that the entire amount of cyclohexane is involved in the phase separation. It is supposed that a small level of miscibility after phase separation would result in closer agreement of dielectric constants measured and predicted. Dielectric constant values as low as 2.5 are measured for macroporous cyanurates prepared with 20 wt % cyclohexane. 

The mean-square dipole moments of POE and POMg are determined from dielectric constant measurements on dilute solutions in benzene. The values obtained are in good agreement with those predicted using the RIS models for these chains. In addition, the unperturbed dimensions of POMg are calculated as a function of molecular weight using the RIS theory. 

Samples of polyd,3-dioxocane) (-Ch OICf lsO-I and poly(1,3-dioxonane) [-Ch OICh lgO-] are prepared, and fractions of both polymers are studied in solution by means of dielectric constant measurements from 20 to 60°C. Mean-square dipole moments thus obtained are compared with theoretical results based on the RIS models of the two chains. Good agreement is obtained. 

Mean-square dipole moments of polylthiodiethylene gycol), an alternating copolymer of ethylene oxide and ethylene sulfide, are determined from dielectric constant measurements on dilute solutions of the polymer in benzene. Since the configuration-dependent properties of one of the parent homopolymers, PES, are unknown, because of its insolubility in ordinary solvents, the results are preferably compared with those of POE chains. It is found that the dipole moments of polylthiodiethylene glycol) are somewhat larger than those of POE. 

Dielectric constant measurements in carbon tetrachioride and in benzene are used to obtain dipole moments of atactic polypropylene sulfide) chains of sufficiently low molecular weight that excluded volume effects are absent. The results are in very good agreement with RIS calculations. Comparison with previously reported experimental results on the high molecular weight polymer confirm the existence of a significant specific solvent effect on the dipole moments. 

Polypropylene sulfide) is synthesized in both the iosotactlc and atactic stereochemical forms. They are investigated by means of dielectric constant measurements in benzene and CCI4. The experimental results are in good agreement with values predicted from RIS calculations. 

The dipole moments of PSDET chains are determined as a function of temperature by means of dielectric constant measurements in dioxane. The experimental results are found to be in fair agreement with theoretical results based on an RIS model in which the required conformational energies are obtained from previous configurational analyses on polylethylene terephthalatei, polyfdiethylene terephthalate), and polylthiodiethylene glycol). 

PCCS and PTCS are synthesized by condensation of the corresponding c/s and Vans isomers of 1,4-cyclohexanedimethanol with sebacic acid. Values of the mean-square dipole moments of both polyesters are determined from dielectric constant measurements on dilute solutions of the polymers in benzene. Theoretical calculations carried out with the RIS model give values of d (In 0) / d Tin very good agreement with the experimental results. Fair agreement between theory and experiment is also found in the case of the dipole moments of the chains. 

Predictive power is poor, so confine searches to easily preparable materials. Use early screening techniques which work on powders like dielectric constant measurements, the Giebe-Scheibe circuit for piezoelectricity and the Kurtz 36,37) powder measurement test for SHG which was "invented" as a result of our pleas for help in finding materials. 

Like conductivity, dielectric constant is strongly dependent on water content. Indeed, the dielectric constant can even be used as a measure of moisture in coal (Chapter 3). Meaningful dielectric constant measurements of coal require drying to a constant dielectric constant, and several forms of coal are used for dielectric constant measurements. These include precisely shaped blocks of coal, mulls of coal in solvents of low dielectric constant, or blocks of powdered coal in a paraffin matrix. 

In multiphase flow metering, it is usually required to distinguish hydrocarbon from water. If the liquid phase is "oil continuous," the water fraction can be determined by dielectric constant measurement at microwave frequencies because the dielectric constant of dry hydrocarbon is on the order of 2 to 4 and that of water is 82. Naturally, density measurement can also distinguish water from oil. The next requirement is to distinguish the flow of liquid from the flow of gas in a system where the two will try to separate and travel at different velocities. Cross-correlation by nuclear techniques can measure the density of the stream twice (a short vertical distance apart) and correlate the fluctuations in density with time to determine velocity. Multiphase flow metering is a new and evolving technology,... 

Polarity is one of the most important parameters of ILs for its effect on electrochemical reactions. It is important when we characterize ILs to measure not only thermal properties such as melting point but also solvent properties such as polarity [68-70]. The most common method of polarity measurement is a dielectric constant measurement. Weingartner et al. and Hefter et al. have shown, by applying appropriately high frequency methods, that the dielectric constants are uniformly around 10-15. Accordingly, the polarity of ILs should be estimated by other methods. Solvatochromism is heavily applied for this purpose due to its simplicity. 

Parkash, S., Armstrong, J.G. 1969. Moisture in butter in relation to dielectric constant measurements. 1. Dairy Sci. 52, 1224-1228. 

The response of the director of a nematic phase to an applied electric field is dependent upon the magnitude of the dielectric permitivity (dielectric constants) measured parallel and perpendicular, and jl respectively, to the director and to the sign and magnitude of the difference between them, Le. the dielectric anisotropy, Aa, see Equation 9 and Figure 2.10. Since the dielectric permitivity measured along the x-axis is unique and the values of the dielectric permitivity measured parallel to the y- and z-axes are the same. 

Table 3.13 Transition temperatures (°C) and some values for the dielectric anisotropy (Ae), the ratio of the dielectric anisotropy and dielectric constant measured parallel to the director fAe/ej. and the ratio of the bend (kjj) and splay (kjj) elastic constants for the nitriles 36, 41, 53, 39,49 and 50... 

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