Conductance measurements dielectric constant

We wanted to be able to correct measurements of dielectric loss (conductance) and dielectric constant of polymerizing styrene solutions for whatever contribution arose from the dead polystyrene present in the solutions. What better way to make polystyrene that was free of all catalyst fragments and polar groups than to irradiate pure, dry styrene Using the same exhaustive drying technique that we were developing for our a-methylstyrene studies, we prepared a batch of pure, dry styrene. This was then to be irradiated under such conditions that approximately 15% conversion to polymer would occur. 

The continuous measurement of moisture in coal has been accomplished by (1) electrical conductivity, (2) dielectric constant, (3) microwave attenuation, (4) neutron scattering, (5) nuclear magnetic resonance, (6) infrared, and (7) thermal conductivity (Hampel, 1974). 

All electrical property values are strongly dependent on water content for water, the dielectric constant is approximately 81 and resistivity is about 106 2 cm. The dielectric constant has been used as a measure of moisture in coal (Speight, 1994, and references cited therein). However, it should be noted that the effect is not considered to be additive due to the different electrical properties of physically and chemically bound water. With an increase in moisture content, electrical conductivity and dielectric constant increase, whereas resistivity and dielectric strength decrease. Hence, except for special purposes (e.g., dielectric strength measurements of underground coal blocks), electrical measurements require the meticulous drying of coal prior to experiments. 

The main advantages of ultrasonic transmitters are the absence of moving parts and the ability to measure the level without making physical contact with the process material. The reading can be unaffected by changes in the composition, density, moisture content, electrical conductivity, and dielectric constant of the process fluid. If temperature compensation and automatic self-calibration are included, the resulting level reading can be accurate to 0.25% of full scale. 

Quantitative measurements of electrokinetic phenomena permit the calculation of the zeta potential by use of the appropriate equations. However, in the deduction of the equations approximations are made this is because in the interfacial region physical properties such as concentration, viscosity, conductivity, and dielectric constant differ from their values in bulk solution, which is not taken into account. Corrections to compensate for these approximations have been introduced, as well as consideration of non-spherical particles and particles of dimensions comparable to the diffuse layer thickness. This should be consulted in the specialized literature. 

It was necessary to measure the dielectric constant and density of each solvent mixture studied. Densities were determined in a constant-temperature bath maintained to within 0.02°C. Gay-Lussac pycnometers with a capacity of 25 mL were used for density measurements. Dielectric constants were determined with a Balsbaugh Model 2TN50 conductivity cell having a cell constant of 0.001. A Janz-Mclntyre a-c bridge (17) was used. The dielectric constants and densities of the solvents are listed in Table I, along with the constants A and B of the Debye-Hiickel theory. 

J. O M. Bockris and J. Bowler-Reed, A Technique for Measuring Dielectric Constants in Conducting Solution, /. Appl. Phys. 2 74 (1951). 

Electrical Properties. The electrical properties of oil and water are quite different in terms of conductivity and dielectric constant (both of which can be related). These differences can be measured accurately with a capacitance probe and correlated to the amount of water in an oil stream. This type of probe is commonly used in on-line situations to monitor percent water in oil pipelines (36, 37). Generally, water and solids cannot be differentiated, so the signal is proportional to the total solids and water content. These systems have seen the greatest applications in monitoring relatively low water contents. In principle, techniques based on electrical properties can be calibrated for process streams with significant water and solids contents. However, the capacitance of the fluid changes with either an increase in solids or an increase in water, so the use of electrical properties in these situations is limited to streams where only one or the other is changing. 

A phase transition at 80 °K was investigated by magnetic susceptibility, low field ESR, dc and microwave conductivity and dielectric constant measurements. The magnetic properties are discussed in terms of a singlet-triplet model above, in terms of ID Heisenberg model below the phase transition. 

Thus, two types of surface charges occur in this case. The first one, Ei, corresponds to the situation in which some charge with density Eq is placed on the interface. In accord with eq. 1.168, such a charge decays exponentially with a time constant Tqs that is controlled by the conductivity and dielectric constant of the medium. Inasmuch as the relaxation time Tqs is usually very small with respect to measurement times, we will no further consider this type of charge and concentrate on the second type. 

Remarkably, the C02/water/Mn(PFPE)2 emulsion system is CO2-continuous up to 50% water by volume. As shown in Figure 2.4-9, conductivities for the entire emulsion are as low as six orders of magnitude less than those of the aqueous phase, clearly suggesting that the emulsions are CO2-continuous. Dielectric data support this assertion as well. The measured dielectric constants for the emulsion remain not far above those of CO2, from 1.6 to 1.7, even at 50% by volume water. These opaque emulsions look like white milk. 

The measurements of conductivities and dielectric constants furnish data for the computation of concentrations of the diflFerent types of defects as a function of solute concentration and of temperature, as well as interpretations in terms of lattice position, thermodynamics, and kinetics of these defects (77, 79). The quantitative evaluation of these measurements depends critically on the determination of the proton mobility, ion concentration, and dissociation constant in pure ice (Table IV) made by Eigen and coworkers (46, 47). 

Figure 18, Frequency dependence of the a-c conductivity and of the dielectric constant after Steinemann (140), (1) Pure ice, (2) Slightly impure ice, (a) Conductivity, (b) Dielectric constant. Curves for pure ice closely follow Equations 12a and 14, except for an incipient low-frequency dispersion that may result from very slight impurity content or from electroae polarization. Debye dispersion between 10 and 10 cps. As the impurity content increases (curves 2), the low-frequency dispersion (Steinemann s F dispersion) becomes more prominent and tends to coalesce with the Debye dispersion. Interpretation then becomes difficult. At still higher concentrations, the two dispersions separate again (see Ref. 140). A slight anisotropy of the dielectric constant, observed by Decroly et al. (34) for measurements parallel and perpendicular to the c axis of single crystals, has not been considered...

What about the detection behavior of QCM if applied in solutions that is, does the deposited material have viscoelastic properties In 1981 Nomura and lijima first reported the QCM measurement in liquid medium. Since then much effort has been devoted to measuring QCM in solution. It appears that the frequency of quartz changes with the density, viscosity, conductivity, and dielectric constants of the solution studied. In addition the roughness of deposition materiaP and the nature of the electrode " used on the quartz s surface can affect the frequency of QCM. The Sauerbrey expression in (14.1) is therefore modified... 

The microwave fi equency conductivity and dielectric constant were measured using the cavity perturbation technique [90,114,142,143]. The resonant cavity used was cylindrical with a TMoio frequency of 6.5 GHz. The entire cavity is inserted into a dewar filled with He gas to provide a temperature range of 4.2-300 K. Alternatively, the microwave fi-equency conductivity and dielectric constant may be measured using a microwave impedance bridge [144]. 

One of the first on-line liquid chromatography detectors to be developed in the early forties was, in fact, a bulk property detector, the refractive index detector (1). Bulk property detectors continuously monitor some physical property of the column eluent and by the use of a suitable transducer provide a voltage - time output that is either proportional to the physical property being measured, or made proportional to the concentrations of the solute eluted. The properties of the mobile pheuse that are most commonly monitored in commercially available bulk property detectors are refractive index, electrical conductivity, and dielectric constant, the dielectric constant detector being the least popular of the three. 

Most work to date has concentrated on a particular aspect of microwave properties, e.g. conductivity or dielectric constant, with few studies of the complete spectrum of properties over broad frequency ranges. For example. Fig. 12-2a.b show the DC vs. microwave (6.5 GHz) conductivity and the microwave (6.5 GHz) dielectric constant vs. temperature for a series of poly(anilines) measured by Javadi et al. [195]. The behavior observed- microwave conductivity greatly exceeding DC conductivity for higher doping levels, and dielectric constant being independent of temperature for low doping levels- is typical of CPs. Buckley and Eashoo [430] obtained relatively poor values for e and e", ca. 90 and 60 (at the Ka band, ca. 33 GHz) for compacted P(Py)/Cl powder. 

Alkyl Halides. Conductance and dielectric-constant measurements indicate the formation of ionic complexes between the catalyst and the alkyl halide ... 

Dielectric Film Deposition. Dielectric films are found in all VLSI circuits to provide insulation between conducting layers, as diffusion and ion implantation (qv) masks, for diffusion from doped oxides, to cap doped films to prevent outdiffusion, and for passivating devices as a measure of protection against external contamination, moisture, and scratches. Properties that define the nature and function of dielectric films are the dielectric constant, the process temperature, and specific fabrication characteristics such as step coverage, gap-filling capabihties, density stress, contamination, thickness uniformity, deposition rate, and moisture resistance (2). Several processes are used to deposit dielectric films including atmospheric pressure CVD (APCVD), low pressure CVD (LPCVD), or plasma-enhanced CVD (PECVD) (see Plasma technology). 

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