Dielectric properties, polymeric

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

The nonlinear optical and dielectric properties of polymers find increasing use in devices, such as cladding and coatings for optical fibres, piezoelectric and optical fibre sensors, frequency doublers, and thin films for integrated optics applications. It is therefore important to understand the dielectric, optical and mechanical response of polymeric materials to optimize their usage. The parameters that are important to evaluate these properties of polymers are their dipole moment polarizability a, hyperpolarizabilities 0... 

In this study, the plasma polymerization and the discharge phenomena were studied as a function of the discharge frequency. In order to support the speculation of the polymerization mechanism, infrared spectra and the dielectric properties were also measured for the samples formed in the same discharge frequency range. 

The molecular stracture and morphology of the film may be affected by the polymerization mechanism. The infrared spectra and dielectric properties were measured in order to correlate with the polymerization mechanisms. 

Among the polyesters that are used for PVC, the copolymers of butadiene with ethyl fumarates and ethyl acrylates deserve mention. They have been produced by Badische Anilin-und Sodafabrik (BASF) under the commercial name Palamoll. Palamoll I consists of 75% diethyl fumarate and 25% butadiene Palamoll II contains equal parts of butadiene and ethyl acrylate. In combination with the same amount of liquid plasticizers (such as DOP), films with cold resistance down to — 60°C. can be produced. These products are especially important for cable insulation because of their good dielectric properties. The Palamoll products are produced by emulsion polymerization and can be directly combined with emulsions of PVC. 

In a majority of works on LC polymers, the main attention was paid to the synthesis and structural studies of such polymers. Significantly less information is available on physical properties of LC polymers, especially, when compared to low-molecular liquid crystals. In this chapter some rheological and dielectric properties of polymeric liquid crystals, characteristics of their dynamic properties and intramolecular mobility, are considered. 

Dielectric measurements have been established for nearly three decades as a technique for monitoring the cure of polymeric resins. Dramatic changes in the dielectric properties of the material accompany the transformation of the resin from a viscous liquid to a solid. 

The dielectric properties of organic and polymeric materials are one of their more attractive properties. Table 4 gives the dielectric constants of PMMA and polystyrene which are typical polymer glasses. ... 

Resinous silicones can be made by polymerizing silicones into cross-linked molecules. These resinous materials are used for electrical insulation. They have excellent dielectric properties and are stable at operating temperatures at wffiich the usual organic insulating mate-... 

The calculation of the effect of a liquid on the dielectric properties of foams requires repre ntation of the structure as a polymeric matrix with two-layer ellipsoidal inclusions, one of the layers being a film of sorbed moisture. 

These results reveal that- a plastic foam structure may be considered as a system of thin films and, therefore, support a model of plastic foam morphology namely a matrix system composed of thin polymeric films defining two groups of cells (macro- and microcells). Additional support in favor of this model of plastic foam structure is provided by the studies on the electric properties of plastic foams Among the numerous equations so far advanced for the calculation of the dielectric properties, the expressions which describe the dry foam structure by one of the limiting cases of a matrix system, namely a laminated dielectric structure with layers parallel to the force lines of the electrical field, agree best with the experiments >. 

Use Polymerizes to form heat-resistant and insulating resins somewhat similar to mica in dielectric properties. 

There has been a great deal of interest in the study of the electrical properties of plasma polymerized films. Early data on the dielectric and conductivity of the films has been reviewed by Mearns ( ). More recently, the dielectric properties of plasma polymerized styrene (69-71), acrylonitrile (72), hexamethyldisiloxane (73-75), tetrafluoroethylene... 

Though polymers made specifically for high voltage insulation are remarkably clean, occasional contaminants occur and contribute to the deterioration of dielectric properties. Some of these are polymeric in nature such as gels or prematurely corsslinked polyethylene particles which may appear amber to dark brown in color depending on heat history. Figure 5 shows one... 

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