Capacitors polymer film

Deposition of thin films is used to change the surface properties of the base material, the substrate. For example, optical properties such as transmission or reflection of lenses and other glass products, can be adjusted by applying suitable coating layer systems. Metal coatings on plastic web produce conductive coatings for film capacitors. Polymer layers on metals enhance the corrosion resistance of the substrate. 

One area where the relationship between the structure of the polymer matrix and the physical processes of the thin layer has been studied in detail is that of electrodes modified with polymer films. The polymer materials investigated in these studies include both conducting and redox polymers. Such investigations have been driven by the many potential applications for these materials. Conducting polymers have been applied in sensors, electrolytic capacitors, batteries, magnetic storage devices, electrostatic loudspeakers and artificial muscles. On the other hand, the development of electrodes coated with redox polymers have been used extensively to develop electrochemical sensors and biosensors. In this discussion,... 

Essentially polymer-film capacitors comprise dielectric films (polymer or paper or both together) interleaved with aluminium electrodes, either as aluminium foil or, more commonly, in the form of a layer evaporated directly on the dielectric, and rolled together. They are sealed in an aluminium can or in epoxy resin. Because the dielectric films and evaporated electrodes have thicknesses of only a few microns and about 0.025 /mi respectively, volumetric efficiencies can be high. The dielectric films are polystyrene, polypropylene, polyester, polycarbonate or paper paper dielectrics are always impregnated with an insulating liquid. 

Ceramic capacitors must either be low in cost in order to compete with polymer-film units or must possess special qualities that assure them of a market. The structure and method of manufacture of a capacitor are governed by a combination of these requirements. 

Electrical grade polymer films have now largely replaced the Kraft paper that was previously used in capacitor applications. Polypropylene and poly(ethylene terephthalate) are both used in capacitors as free films or metallized with a thin layer of aluminum. Other, newer materials for capacitor applications are made by metallizing polysulfone and polycarbonate films. 

The main commercial use of solid SiO is as a vapor-deposition material for the production of SiOx thin films for optical or electronic applications (antireflective coatings, interference filters, beam-splitters, decorative coatings, dielectric layers, isolation layers, electrodes, thin-film capacitors, thin-film transistors, etc.), for diffusion barrier layers on polymer foils or for surface protection layers.Other uses for SiO have been proposed, such as the substitution of elemental silicon in the Muller-Rochow process for the production of organosilicon halides, because solid SiO can be produced at lower temperatures than elemental silicon. 

As charge is inserted or removed at low rates, the polymer film behaves as a (redox) capacitor. The redox capacity of electroactive films is a quantity of fundamental importance, and it may be determined by several complementary techniques including cyclic voltammetry, electrochemical impedance and coulometric titration. Cyclic voltammetry of a redox polymer film at a slow... 

Another contacting thickness measurement is the capacitance measurement. Metal plates are placed at either side of the polymer film. Thus, the material and plates form a capacitor, with the polymer acting as a dielectric. Since the capacitance depends on the thickness of the dielectric, the material thickness is determined by measuring the capacitance. The problem in applying this technique to extrusion is that it will be difficult to establish good contact between polymer and metal plates, particularly in continuous monitoring of thickness. 

A pH sensor, based on a.c. conductivity measurements of a thin polymer film, has been developed. The sensor consists of a planar interdigitated electrode array coated with a polypyrrole multilayer, built-up using the Langmuir-Blodgett technique. Impedance spectroscopy has been used to investigate the complex admittance of the device when exposed to aqueous solutions of different pH. The experimental data have been fitted to the theoretical response of an equivalent electrical network of capacitors and resistors. A response over the pH range 3.5 to 8 has been measured. 

Field-induced reorientation of the director with attendant optical changes has recently been used in a novel application with the potential for large-area LCDs polymer dispersed LCs (PDLCs). A PDLC is a microemulsion of MLC dispersed in a conventional transparent polymer film. In the off state there is a mismatch between the refractive index of the MLC and that of the host polymer film. Hence the dispersion of MLC droplets scatters light very effectively, giving an optically opaque film (Fig. 5.14, left-hand side). On application of an external electric field (across a capacitor-like transparent coating of tin oxide on both sides of the polymer film), the director assumes the same orientation in all of the microdroplets. If the... 

Early capacitors were usually made with paper or mica. Paper was used for large capacitance values and mica was used for high-frequency capacitors. With the advent of commercial polymer film production, these increasingly available materials became popular as capacitor dielectrics. Polymer films are ideally suited for capacitor manufacture because they ... 

Many polymer films have been examined as capacitor dielectrics but those principally used are polyethylene terephthalate, polystyrene, polycarbonate, polytetrafluoroethylene, polyimides and polypara-xylylene. A number of these materials are more familiar by their trade names ... 

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