Fluids dielectric properties

Sihcone fluids have good dielectric properties, loss factor, specific resistance, and dielectric strength at normal operating conditions, and the properties vary only slightly with temperature (59,328,350). The properties in combination with relatively low flammabiUty have led to the use of siUcones in transformers and other large electrical appHcations (351). The dielectric constant of a 1000-cSt oil is 2.8 at 30°C and 2.6 at 100°C. The loss factor is low,... 

PollockEL, Alder BJ, Patey GN (1981) Static dielectric properties of polarizable Stockmayer fluids. Physica A Stat Theor Phys 108(1) 14—26... 

In general, the properties of supercritical fluids make them interesting media in which to conduct chemical reactions. A supercritical fluid can be defined as a substance or mixture at conditions which exceed the critical temperature (Tc) and critical pressure (Pc). One of the primary advantages of employing a supercritical fluid as the continuous phase lies in the ability to manipulate the solvent strength (dielectric constant) simply by varying the temperature and pressure of the system. Additionally, supercritical fluids have properties which are intermediate between those of a liquid and those of a gas. As an illustration, a supercritical fluid can have liquid-like density and simultaneously possess gas-like viscosity. For more information, the reader is referred to several books which have been published on supercritical fluid science and technology [1-4],... 

Steady-State Fluorescence. The fluorescence characteristics of PRODAN are extremely sensitive to the physicochemical properties of the solvent (38). As benchmarks, the steady-state emission spectra for PRODAN in several liquid solvents are presented in Figure 1. It is evident that the PRODAN emission spectrum red shifts with increasing solvent polarity. This red shift is a result of the dielectric properties of the surrounding solvent and the large excited-state dipole moment (ca. 20 Debye units) of PRODAN (38). It is the sensitivity of the PRODAN fluorescence that will be used here to investigate the local solvent composition in binary supercritical fluids. 

These formulas were previously used for all possible ranges of the cone angles— that is, for p [0,7t/2], but without theoretical justification. Because of the simplicity of Eq. (126a) in comparison with the formulas for the spectral function pertinent to the rigorous hat-plane model (see Section IV.C.3), the hybrid model was often applied for calculation of dielectric properties of various polar fluids. 

The profile (160) is illustrated by Fig. 20 for the parameters typical for water in this Figure the flat part 2(3/ and the total angular width 2(3 are shown. The rectangular profile, with which the dielectric properties of fluids were previously rather successfully studied (VIG) [3, 7], corresponds to / = 1 (see also Section IV). 

E. L. Pollock, B. J. Alder and G. N. Patey, Static dielectric properties of polarizable Stock-mayer fluids, Physica A, 108 (1981) 14—26. 

A. Water and Tissue Water. The dielectric properties of pure water have been well established from dc up to microwave frequencies, approaching the infrared (3). For all practical purposes they are characterized by a single relaxation process centered near 20 GHz at room temperature. Static and infinite frequency permittivity values are, at room temperature, close to 78 and 5, respectively. Hence, the microwave conductivity increase predicted by Eq. (1) is close to 0.8 mho/cm above 20 GHz, much larger than typical low-frequency conductivities of biological fluids which are about 0.01 mho/cm. The dielectric properties of water are independent of field strength up to fields of the order 100 kV/cm. 

Low frequency dielectric properties of liquid and solid water. In The Liquid State of Matter Fluids, Simple and Complex, pp. 341 31, Amsterdam North-Holland (1982). 

P. J. Fortune, P. R. Certain, and L. W. Bruch. Helium diatom polarizability and the dielectric properties of fluid helium. Chem. Phys. Lett., 27 233-236 (1974). 

B. J. Alder, H. L. Strauss, and J. J. Weis. Dielectric properties of fluids composed of spheres of constant polarizability. J. Chem. Phys., 62 2328-2334 (1975). 

Commonly, the thickening of liquids by hydrophilic silica is explained by the formation of H-bonds between the silanol groups of silica particles [6]. According to this model, the stability of silica gels in styrene and toluene, two fluids with comparable dielectrical properties, should be more or less identical. Figure 2 depicts the shear yield-stress experiments using the vane geometry of HDK N20 in styrene and toluene. 

Nernst applied the electrical bridge invented by Wheatstone to the measurement of the dielectric constants for aqueous electrolytes and different organic fluids. Nemst s approach was soon employed by others for measurement of dielectric properties and the resistance of galvanic cells. Finkelstein applied the technique to the analysis of the dielectric response of oxides. Warburg developed expressions for the impedance response associated with the laws of diffusion, developed almost 50 years earlier by Fick, and introduced the electrical circuit analogue for electrolytic systems in which the capacitance and resistance were functions of frequency. The concept of diffusion impedance was applied by Kruger to the capacitive response of mercury electrodes. ... 

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