Electrically conducting polymer films

HDPE, composite materials such as epoxy-glass fiber and epoxy-carbon fiber, and laminate structures such as polymer films on bulk metal substrates. Thin-conductive film heaters were made of electrically conductive paints, electrically conductive polymer films, metal foils (stainless-steel, copper, titanium, and titanium alloys), and thin metal films sputtered on a ceramics or glass. The samples dimensions varied from a few centimeters to 5m. 

There are several methods used to modify electrode surfaces adsorption of reagents on the surface, covalent bonding by reaction between the modifier and functional groups on the electrode surface, incorporation of the modifier within a gel or an electrically conducting polymer film, physically coaling the electrode surface with the modifier, e.g., an enzyme, or mixing the modifier with carbon paste. 

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. 

Polypyrroles. Highly stable, flexible films of polypyrrole ate obtained by electrolytic oxidation of the appropriate pyrrole monomers (46). The films are not affected by air and can be heated to 250°C with Htde effect. It is beheved that the pyrrole units remain intact and that linking is by the a-carbons. Copolymerization of pyrrole with /V-methy1pyrro1e yields compositions of varying electrical conductivity, depending on the monomer ratio. Conductivities as high as 10 /(n-m) have been reported (47) (see Electrically conductive polymers). 

Electrically conducting polymer particles such as polypyrrole and polyaniline could also be prepared by dispersion polymerization in aqueous ethanol (31). The oxidation polymerization of pyrrole and aniline has been carried out at the electrode surfaces so far and formed a thin film of conducting polymer. On the other hand, polypyrrole precipitates as particles when an oxidizing reagent is added to a pyrrole dissolved ethanol solution, which contains a water-soluble stabilizer. In this way electrically conducting polymer particles are obtained and, in order to add more function to them, incorporation of functional groups, such as aldehyde to the surface, and silicone treatment were invented (32). 

The report of the doping of polyacetylene (PAc) films to produce metallic levels of conductivity by Shirakawa et al. (1977) sparked the interest in electrically conductive polymers that has continued until today. While it was not the first example of a conductive polymer, the increase in conductivity, by a factor greater than 107, observed on exposing films of trans-PAc to arsenic pentafluoride and iodine, was dramatic, see Fig. 9.1. The impact of this result was immediate, and created an upsurge of interest in conjugated polymers and the possibility of rendering them conductive. 

Waltman, R. J. Bargon, J. Electrically conducting polymers a review of the electropolymerization reaction, of the effects of chemical structure on polymer film properties, and of applications towards technology. Canad. J. Chem. 1986, 64, 76-95... 

Electrically conductive polymer composites were made by dispersing TCNQ salt in polymer matrices. Composite film conductivity and stability are discussed in terms of charge-transfer interaction between TCNQ salt and matrix polymer and the resulting film morphology. The extent of CT interaction and tendency of microcrystallization of TCNQ salt in the matrices were determined by visible spectra. Conductivity and stability are morphology dependent of the film high conductivity requires a uniform, densely packed dispersion of TCNQ salt microcrystallites. The highest conductivity was always attained at [TCNQ°]/[TCNQ ]sl. 

Given the nature of the polymer and the conduction pathway, a simple homogeneous model cannot be applied to thin conducting polymer film-electrolyte systems [27,28,31]. For thin films (< lOOnm) with pore sizes estimated to range from 1 to 4 nm, the porous surface-electrolyte interface will dominate the electrical and physical properties of the sensor. Since the oxidation of the porous surface occurs first, the interface properties play a major role in determining device response. To make use of this information for the immunosensor response, the appropriate measurement frequency must be chosen to discriminate between bulk and interface phenomena. To determine the optimum frequency to probe the interface, the admittance spectra of the conducting polymer films in the frequency range of interest are required. 

The common electrically conductive polymers can generally be prepared in film form, however, not thermoplastic. In several cases, the conducting polymers are brittle and thus have marginal mechanical utility. Blends with thermoplastics have been studied to search for solutions to these problems. 

The electron transfer rate can be improved by using an electrically conductive polymer like polypyrrole [16] as an interface between the electrode and the non-conductive polymer matrix bearing the glucose oxidase and the mediator. Even better results can be achieved in a copolymerization of enzyme and mediator into a polypyrrole film on top of a platinum electrode [17, 18]. Here, the mediator ferrocene is copolymerized with the pyrrole. 

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