Voltage breakdown, polymer electricity

The thickness and density of electrically deposited layers are a function of the dielectric properties of the powder composition and the process parameters. Common to all electrostatic deposition techniques of polymer powders is the existence of some critical thickness of the deposited layer. As soon as this is reached, no particles are deposited any more because of the Coulomb repulsion of the approaching unipolar charged particles by the layer. An effect called inverse corona appears in the layer, which means that voltage breakdown occurs in it as a result of raised field intensity, which ionizes the air between the particles, and a flow of ions is generated from the substrate with a charge opposite to that of the particles being deposited. This abruptly slows down the deposition and leads to uneven thickness of the deposited layer, formation of numerous craters and through pores. 

Although the literature on electrodeposited electroactive and passivating polymers is vast, surprisingly few studies exist on the solid-state electrical properties of such films, with a focus on systems derived from phenolic monomers, - and apparently none exist on the use of such films as solid polymer electrolytes. To characterize the nature of ultrathin electrodeposited polymers as dielectrics and electrolytes, solid-state electrical measurements are made by electrodeposition of pofy(phenylene oxide) and related polymers onto planar ITO or Au substrates and then using a two-electrode configuration with a soft ohmic contact as the top electrode (see Figure 27). Both dc and ac measurements are taken to determine the electrical and ionic conductivities and the breakdown voltage of the film. 

The electrical properties of materials are important for many of the higher technology applications. Measurements can be made using AC and/or DC. The electrical properties are dependent on voltage and frequency. Important electrical properties include dielectric loss, loss factor, dielectric constant, conductivity, relaxation time, induced dipole moment, electrical resistance, power loss, dissipation factor, and electrical breakdown. Electrical properties are related to polymer structure. Most organic polymers are nonconductors, but some are conductors. 

Several tests are essential for the evaluation of plastics in electrical applications. These tests include dielectric constant (permittivity ASTM-D150-74), which is the ratio of the capacitance of the polymer compared to air, dielectric strength, and dielectric breakdown voltage (ASTM-D149-75). Dielectric breakdown voltage is... 

The dielectric strength of PES, as measured in oil by the short term tests ASTM D 149, is 800 KV/em for a 0.23 mm section and 158 KV/cm for 3 2.3 mm. The tracking behaviour of PES when subjected to high voltages is very complex and this phen< nenon is currently under investigation. There are indications that electrical breakdown associated with carbonisation tends to occur across the surface of the material. However, results obtained are similar to those found for other amorphous aromatic polymers like polycarbonate. 

Dielectric strength (electric strength) n. A measure of the voltage required to puncture an insulating material, expressed in volts per mil of thickness (SI V/rrmi). The voltage is the root-mean-square voltage difference between the two electrodes in contact with opposite surfaces of the specimen at which electrical breakdown occurs under prescribed test conditions. Ku CC, Liepins R (1987) Electrical properties of polymers. Hanser Publishers, New York. Weast RC (ed) (1971) Handbook of chemistry and physics, 52nd edn. The Chemical Rubber Co., Boca Raton, FL. 

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