Electrical Conduction Mechanisms polymer

Attempts have recently been made to determine the dominat electric conductivity mechanism using the results of measurements of the current flow across asymmetric systems, such as metal -polymer-metalo (Me -P-Mc2) and metal-polymer-semiconductor (M-P-Sj such studies involved plasma-polymerized styrene (2 ), silo-xane and silazane ( ). The possibility of tunnel-... 

The mixing of neutral polymers with particles of conductive substances like metals or carbon black for the purpose of modifying the electrical conductivity of polymers has been demonstrated in many works. Electric conduction in such composite materials is achieved due to contacts between the conductive particles dispersed in the polymeric matrix. In order to obtain continuous conductive paths in such a system the quantity of the additive has to be relatively large. However, the presence of these additives has an undesirable effect on the mechanical properties of the composite. ... 

Kim, I. H., and Jeong, Y G. (2010], Polylactide/exfoliated graphite nanocomposites with enhanced thermal stability, mechanical modulus, and electrical conductivity. J. Polym. Sci. Polym. Phys., 8, pp. 850-858. 

Zero-dimensional defects or point defects conclude the list of defect types with Fig. 5.87. Interstitial electrons, electron holes, and excitons (hole-electron combinations of increased energy) are involved in the electrical conduction mechanisms of materials, including conducting polymers. Vacancies and interstitial motifs, of major importance for the explanation of diffusivity and chemical reactivity in ionic crystals, can also be found in copolymers and on co-crystallization with small molecules. Of special importance for the crystal of linear macromolecules is, however, the chain disorder listed in Fig. 5.86 (compare also with Fig. 2.98). The ideal chain packing (a) is only rarely continued along the whole molecule (fuUy extended-chain crystals, see the example of Fig. 5.78). A most common defect is the chain fold (b). Often collected into fold surfaces, but also possible as a larger defect in the crystal interior. Twists, jogs, kinks, and ends are other polymer point defects of interest. 

Bipolar plates are the components performing a number of tasks such as reactant supply, heat exchange, electron transfer to the external circuit, physical strengthening of the cell, etc. The material requirements for bipolar plates include high mechanical strength, corrosion resistance, electronic conductivity, low density, etc. [154]. CNT/polymer compos-ites-based bipolar plates enhance the fuel cell performance considerably [155,156]. The relevant properties such as electrical conductivity, mechanical strength, contact resistance and chemical inertness of the composites exhibit large improvements in PEM fuel cells [157-159]. 

Although most of the everyday, high-tonnage polymers in present use are insulators, this book is devoted to an important class of recently developed polymers that conduct. Many polymeric materials can be formed into thin, mechanically strong films, and it is obviously desirable to confer the additional property of electrical conductivity on polymers that already benefit from being flexible and compact. Consequently, much ingenuity has been displayed over the past decade or more in developing plastic and elastomeric materials which conduct ions and/or electrons [1-5]. 

In the solid state, the electrical conductivity of polymer-carbon nanotube composites can be affected by various external stimuli like changes in temperature [68], mechanical stress [69], and exposure to liquids [49,70,71] or organic vapor compounds [72-74]. These sensitivities may be exploited for the creation of smart components [75]. 

Rarkhutik, V., Ratil, R., Harima, Y. and Matveyeva, E. (2006) Electrical conduction mechanism in conjugated polymers studied using flicker noise spectroscopy. Electrochimica Acta, 51, 2656-1661. 

Since the majority of polyiimrs are scmicrystalline, their electrical conduction mechanism is more complex than fo inorganic ordered materials. (TOnductioo in polymers may also depend on sample preparation and history. As a consequence, different conduction mechanisms have been repotted for the satxK material (103,125,146.147). The conductivity of polymers varies exponentially with temperatures and can be expressed as... 

In this chapter, the recent advances in the field of carbon nanotube/polymer nanocomposite aerogels and related materials are described. An emphasis is paid to the relationship between the preparation method and the most characteristic properties of these materials such as density, surface area, electrical conductivity, mechanical strength, and so forth. 

Cotts, D. B. and Z. Reyes, Electrically Conductive Organic Polymers for Advanced Applications , Noyes, Park Ridge, NJ, 1986. The properties of about 250 electrically conducting, semiconducting and semi-insulating polymers were surveyed and their conduction mechanism, mechanical properties and suitability for space-based use was evaluated. 

ELECTRIC CONTACT PERFORMANCES AND ELECTRICAL CONDUCTION MECHANISMS OF AN ELASTOMERIC CONDUCTIVE POLYMER... 

The conductive polymer is usually composed of dispersed electrically conductive particles such as carbon black or metal in a durable polymer matrix such as silicone rubber. As it is possible to obtain conductivity and elasticity in simple materials, this is useful for high density micro-sized electrical contacts as connector or as key-board switch. However, in spite of the excellent properties, it is difficult to obtain low electrical resistivity. In order to approach this problem, performances of the contacts between the polymer surface and metal were studied from the view point of surface contamination. The electrical conduction mechanism and a method to get low resistivity were also studied. The results show that the surface of the polymers containing carbon black shows contamination resistance properties because of their chemical stability. The conduction mechanism changes with particle content. For large content, electric current flows through particles contacting each other and for small content, the current passes through the gap between particles by Schottky conduction. Thus, as the resistance consists of particle resistance, constriction resistance and gap resistance, the resistance can be controlled by particle material, their content and size. 

For the electrically conducting mechanism of polymer composites, two key questions are associated (1) how to form the conducting paths and (2) how to conduct after the formation of the paths. Concerning the second question, there... 

The successfiil synthesis of a transparent soHd polymer electrolyte (SPE) based on PEO and alkoxysilanes has been reported (41). The material possessed good mechanical properties and high electrical conductivity (around 1.8 x 10 S/cm at 25°C) dependent on the organic—inorganic ratio and PEO chain length. 

Whilst the conductivity of these polymers is generally somewhat inferior to that of metals (for example, the electrical conductivity of polyacetylenes has reached more than 400 000 S/cm compared to values for copper of about 600 000 S/cm), when comparisons are made on the basis of equal mass the situation may be reversed. Unfortunately, most of the polymers also display other disadvantages such as improcessability, poor mechanical strength, poor stability under exposure to common environmental conditions, particularly at elevated temperatures, poor storage stability leading to a loss in conductivity and poor stability in the presence of electrolytes. In spite of the involvement of a number of important companies (e.g. Allied, BASF, IBM and Rohm and Haas) commercial development has been slow however, some uses have begun to emerge. It is therefore instructive to review briefly the potential for these materials. 

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