Polymers electrical breakdown

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. 

Most siloxane polymers are excellent insulators, and electrical properties relevant to this characteristic are also much studied. Examples are resistivity, dielectric constant, dielectric losses, dielectric strength (resistance to electrical breakdown), and power factors.16... 

Recent applications of FNS include the dynamics of the electrical potential fluctuation in an electromembrane system [iv], analysis of the fluctuations of the electrical current in electrochemically deposited conducting polymers [v], and forecasting electrical breakdown in porous silicon [vi]. 

In the following sections we discuss briefly the principal mechanisms of electrical breakdown in solid polymers and some of the consequences for the use of these as insulating materials. A brief outline of the statistical treatment of breakdown data is given in the appendix (Section 6.9). 

Resistance of plasma-polymerized films with respect to electric breakdown can be quite high. This resistance increases at relatively low specific powers of the non-thermal discharges applied for polymer film deposition. As an example, plasma-polymerized fluorocy-clobntane film is characterized by breakdown electric fields 5 10 V/cmforafihnthickness of 150 nm, 6 10 V/cm for a film thickness of 100 nm, and 7-8 10 V/cmforafihnthickness of 75 nm. To compare, breakdown of a conventional PTFE film with thickness 0.1-... 

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. 

Principles and Characteristics Laser ablation is conceptually very simple, but mechanistically complicated. The process involves coupling of the photon energy of a laser pulse (typically about 20-30 ns wide, with an energy of 1-10 Jcm ) into the surface of a solid, resulting in evaporation and ejection of various species from the surface (the so-called plume ) within 10 to 10 s. The first experiments were carried out in 1962 [32]. When focused to a small area, a laser beam provides enormous power densities and electromagnetic fields. The plume , presumably a plasma, is accompanied by shock waves and electrical breakdown. The ejected material may eventually be deposited as a thin film. It is possible, by suitable selection of laser power and focus, to ablate a range of plastic materials in a controlled manner. For some matrices the polymer melts and diffuses away from the centre of the ablation site, leading to the forma-... 

The application of high fields to charge or polarize polymer electrets inherently involves the risk of sample damage due to electrical breakdown. While local air breakdown in voids is part of the poling process, energy-rich discharges over large areas of ferroelectric polymers will lead to sample failure. 

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