Electrically Conductive Modifier

Often there is a need to drain or dissipate electrical charges off polymeric surfaces. Aramids are likely to collect electrical charges. Therefore, there is an inherent threat of sparking on discharge. Sulfonated poly(anihne) can be added to aramid in order to increase the electrical conductivity.  

The electrically conductive composites prepared by these methods are not sufficiently conductive for shielding of electromagnetic interference. Still more effective in producing conductive aramids is electroless plating. A high electrically conductive fiber is obtained. The fiber is impregnated with metal complexes using supercritical carbon dioxide. 

The metal complexes are activated by reduction in hydrogen and then immersed into an electroless plating solution. The process has been using palladium(II)-hexafluoroacetylacetonate. The palladium complex can be activated in the absence of hydrogen. This reduces the risks of explosion in a technical process. 

Aramid fibers are notorious for their application in bulletproof jackets, more generally addressed as ballistic resistant fabric articles. Less exciting applications of aramids are in automotive, electrical, and electronic fields. They are also used in medical devices. Specific uses are summarized in Table 13.3. 

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Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

Early models used a value for that remained constant throughout the day. However, measurements show that the deposition velocity increases during the day as surface heating increases atmospheric turbulence and hence diffusion, and plant stomatal activity increases (50—52). More recent models take this variation of into account. In one approach, the first step is to estimate the upper limit for in terms of the transport processes alone. This value is then modified to account for surface interaction, because the earth s surface is not a perfect sink for all pollutants. This method has led to what is referred to as the resistance model (52,53) that represents as the analogue of an electrical conductance... 

Figure 12 contrasts the decrease in conductivity of ETP copper with that of oxygen-free copper as impurity contents are increased. The importance of oxygen in modifying the effect of impurities on conductivity is clearly illustrated. Phosphoms, which is often used as a deoxidizer, has a pronounced effect in lowering electrical conductivity in oxygen-free copper, but Httie effect in the presence of excess oxygen. 

Fluorine doping modifies the optical properties and is accomplished by the addition of CFjBr in the gas stream. Doping results in a considerable increase in electrical conductivity with a resistivity as low as S.IO " Qcm.P2]... 

The two extremes of ordering in solids are perfect crystals with complete regularity and amorphous solids that have little symmetry. Most solid materials are crystalline but contain defects. Crystalline defects can profoundly alter the properties of a solid material, often in ways that have usefial applications. Doped semiconductors, described in Section 10-, are solids into which impurity defects are introduced deliberately in order to modify electrical conductivity. Gemstones are crystals containing impurities that give them their color. Sapphires and rubies are imperfect crystals of colorless AI2 O3, red. 

Polyvinyl chloride has been modified by photochemical reactions in order to either produce a conductive polymer or to improve its light-stability. In the first case, the PVC plate was extensively photochlorinated and then degraded by UV exposure in N2. Total dehydrochlorination was achieved by a short Ar+ laser irradiation at 488 nm that leads to a purely carbon polymer which was shown to exhibit an electrical conductivity. In the second case, an epoxy-acrylate resin was coated onto a transparent PVC sheet and crosslinked by UV irradiation in the presence of both a photoinitiator and a UV absorber. This superficial treatment was found to greatly improve the photostability of PVC as well as its surface properties. 

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