Dielectric permittivity measurements

When applying an alternating electric field to a polymer placed between two electrodes, the response is generally attenuated and the output current is out of phase compared with the input voltage. This response stems from the polymer s capacitive component and its conductive or loss component, as represented by a complex dielectric permittivity measured frequencies f, and temperatures T ... 

Klein, K. and Santamarina, J.C. (1997) Methods for broad-band dielectric permittivity measurements (soil-water mixtures, 5 Hz to 1.3 GHz), ASTM Geotechnical Testing Journal 20, 168-178... 

Or, D. and Wraith, J.M. (1999) Temperature effects on soil bulk dielectric permittivity measured by time domain reflectometry A physical model, Water Resources Research 35 Suppl. 2, 371-383... 

Much of the research on solvation dynamics has been devoted to polar solute-solvent systems. In these media, it has been found that the response to a change in solute dipole is due primarily to collective solvent reorientation and that it can be predicted reasonably well using information on pure solvent dipolar reorientation, for example, from dielectric permittivity measurements, as input [1,6,7,9],... 

In this equation is the dielectric permittivity measured at infrared or micro-wave frequencies, which is up to five times higher than op. This dielectric permittivity has a very significant influence on the final values of Tl (see Eq. (37)). 

Another very typical surfactant for the formation of W/O microemulsions is AOT [sodium bis(2-ethylhexyl) sulfosuccinate], and such systems have been intensively studied. For instance, viscosity of the hard-sphere type has recently been reported for a W/O microemulsion made up from water, AOTand hydrocarbon, and the relative viscosity equals those of latex or silica spheres of corresponding volume fraction [59]. However, here the situation is somewhat more complicated, since at higher concentrations and higher temperatures attractive interactions lead to a reversible aggregation of the droplets that has to be taken into account [60]. This clustering process (which has also been evidenced via other methods such as dielectric permittivity measurements [61] and dynamic Kerr effect experiments [62] leads to an increase in the relative viscosity with rising temperature. 

Abstract The physical principles and basic experimental techniques of impedance spectroscopy, i. e. static or frequency dependent dielectric permittivity measurements of sorbent/sorbate systems are given. These measurements can be used to characterize the state of a sorbent material in industrial adsorption processes. Combined with either manometric or gravimetric measurements of adsorption equilibria leading to calibration curves, permittivity measurements also allow fairly simple and quick measurements of gas adsorption equilibria. Kinetic processes and catalytic reactions inside a sorbent/sorbate system also can be observed. Pros and cons of dielectric measurements are discussed. List of Symbols. References. 

The material presented in this chapter is organized as follows In Sect. 2 the basic experiments necessary for dielectric permittivity measurements is given, followed by an outline of the theory of dielectric polarization, which considers the uncertainties of measurements and gives several examples related to gas adsorption equilibria on microporous solids. In Sect. 3 combined dielectric-manometric and dielectric-gravimetric measurements of adsorption equilibria are considered briefly. In Sect. 4 the pros and cons of dielectric measurements are discussed. A hst of Symbols used is given in Sect. 5 followed by the references cited. 

Figure 6.2. Cylinder capacitor filled with zeolite pellets for dielectric permittivity measurements of gas adsorption equilibria.

According to EQN (3) when li = 0 (non-polar molecules) the dielectric anisotropy is determined by the polarisabilily anisotropy Aa which is always positive for rod-like molecules. For polar molecules (p > 0) the anisotropy As depends on the angle p. The dipole contribution to As is positive for P < 54.7 and negative for p > 54.7 . In the latter case the sign of Ae depends on the relative magnitude of the two contributions. Typical dielectric permittivities measured for substances with different polarities are presented in FIGURE 2. 

Sharma, M.M., Garrouch, A., Dunlap, HJ., 1991. Effects of wettability, pore geometry, and stress on electrical conduction in fluid saturated rocks. Log Anal. 32,511 526. SeptembCT lctober. Sherman, M., 1986. A model for the determination of water saturation from dielectric permittivity measurements. In SPWLA 27th Annual Logging Symposium Transactions, Housttm, Texas, June 9—13. Paper E. 

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