Testing capacitive properties

We measure the capacitive properties of a polymer in a capacitor that is constructed so that we can compare the properties of the test material relative to a vacuum. 

The capacitive properties of nanotubes obtained with Cho et al. s method have been studied by Liu et al. from the same research group.208 Tubular structures were obtained with electrodeposition in acetonitrile solution containing 20 mM EDOT under potentio-static condition at 1.6 V vs. Ag/AgCl while nanofibers were synthesized in lOOmM EDOT and at 1.4 V applied potential. Thin wall nanotubes of PEDOT exhibited a stable specific capacitance of 140 Fg 1, while the specific capacitance for the solid nanofibers was 50Fg 1, under the identical test conditions. Figure 9 compares the... 

In conclusion, SW-CAM allows us to accurately test the properties of capacitive porous carbon electrodes and calculate the electrode capacity and the various contributions to the observed resistance. In this case, the linear (external) resistance determines the total resistance and analysis suggests that we can assign this resistance to the external electrical circuit, while we can also tentatively conclude that the distributed (volumetric) resistance within the electrode may be close to the ideal value based on an ion transport resistance only determined by the free solution ion diffusion coefficients. This finalizes our exposition of the derivation of the various constants in the transmission line theory based on the SW-CAM technique. In conclusion, the SW-CAM technique is a robust, precise, and very informative method to perform EC analysis on two-electrode capacitive cells in aqueous solutions. 

AC, carbon black and aerogel are the first carbon aUotropes tested on supercapacitors and used in industrial type supercapacitor cells. To improve capacitive properties of EDLCs, their carbon-Uke nanostmeture electrodes are modified with electroactive materials. This modification leads to accumulation of additional charge on the electrode surface and improved the capacitance. The carbon materials have been used as additives, catalyst for electron transfer, hosts for intercalation of ions, substrates for electrode materials, and electrodes for energy storage devices [39 1]. ACs have been used with PEDOT as composite for the enhancement of capacitance of supercapacitor cells. Activated carbon/CPs are also used in asymmetric supercapacitors [42-44]. 

For the direct determination of the permittivity of an insulator, a capacitor is constructed in such a way that its vacuum capacitance can be measured or calculated. Ideally, specimens take the form of film or sheet, but tubes can also be accommodated. Electrodes may consist of metal foil or plates, vapor-deposited metal, or conductive liquid. The dielectric of interest is sandwiched between the plates of the capacitor, and the capacitance and dissipation factor of the system are measured. The observed capacitive properties are compared against the vacuum characteristics calculated for the cell configuration, and the permittivity and dissipation factor of the insulator are calculated. Equations applicable to the various capacitor and electrode configurations can be found in the ASTM test method. 

The capacitive properties of thin films and sheets can also be determined in a cell into which a specimen is placed between fixed parallel plate electrodes, thereby displacing a fluid of accurately known dielectric properties. The basic configuration of the test cell used for such measurements is shown in Figure 49. If the thickness of the specimen can be accurately measured, it is only necessary to determine the capacitance and dissipation factor of the cell with a single fluid separating the plates and with the specimen inserted between the plates displacing some of the fluid. If the average thickness of the specimen cannot be accurately measured, as in the case of extremely thin films, two different fluids must be... 

Figure 49 Schematic illustration showing a cross section of a test cell used to measure electrical capacitive properties by fluid displacement procedures.

Additionally, some parameters, such as sensitivity, are influenced by electrical and mechanical effects. This means that designing the sensor has to include not only the sensor s geometry, but also the design of tests that can distinguish between electrical (e.g., capacitance) and mechanical (e.g., stress) properties. Thus, designing for testing is an important issue. 

Electrical properties of grain have been utilized for quick moisture tests based on the measurement of resistance, capacitance, or electrical conductivity. Many studies have been devoted to the development of density-independent functions of the dielectric properties that would permit on-line measurement of moisture content [74-76]. Also, measurements of electrical properties of grain and seed have been employed for purposes other than determining moisture content. For example, viable seeds of corn were sorted from dead seeds by measuring the current conducted by individual soaked kernels between electrodes connected to a 6-V dc source [77]. Another application of electrical properties is electrostatic separation where the ability of a seed to hold a surface charge is determined mainly by its conductivity. 

Techniques for using a silicon-based light addressable potentiometric sensor (LAPS) to measure the electrical properties of phospholipid bilayer membranes were developed. Membrane conductance, capacitance, and potential could all be measured when the membrane was painted on an aperture between the silicon surface and a controlling electrode. The sensor was tested by observing changes in membrane properties on the addition of simple ion carriers and channels. 

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