Conduction, electrically active polymers

The alignment and electrical contacting of NAD -dependent enzymes on electrodes was also accomplished by the generation of the NAD enzytne complex and its crosslinking on a conductive, redox-active, polymer that electrically contacts the cofactor-enzyme assembly with the electrode, Fig. 3-23. 

Chemical or electrochemical oxidation of numerous resonance-stabihsed aromatic molecules, such as pyrrole (9), thiophene (10), aniline (11), furan (12), carbazole (13), azulene (14) and indole (15), produces electronically conducting polymers (2,17-21,53-55) (see Electrically Active Polymers). 

It has been clearly demonstrated over the past 20 years that inherently conducting polymers (ICPs) are capable of providing all of the above functions and as such they have a critical role to play in the development of intelligent polymer systems (see Electrically Active Polymers). 

Oxidative poljnnerization of aniline produces polyanihne (PAN) (eq. 6). This polymer was obtained as aniline black about a century ago (116,117) and has been revived as an electrically conducting polymer (see Electrically Active Polymers). 

In recent several years, super-capacitors are attracting more and more attention because of their high capacitance and potential applications in electronic devices. The performance of super-capacitors with MWCNTs deposited with conducting polymers as active materials is greatly enhanced compared to electric double-layer super-capacitors with CNTs due to the Faraday effect of the conducting polymer as shown in Fig. 9.18 (Valter et al., 2002). Besides those mentioned above, polymer/ CNT nanocomposites own many potential applications (Breuer and Sundararaj, 2004) in electrochemical actuation, wave absorption, electronic packaging, selfregulating heater, and PTC resistors, etc. The conductivity results for polymer/CNT composites are summarized in Table 9.1 (Biercuk et al., 2002). 

The discovery that doped forms of polypyrroles conduct electrical current has spurred a great deal of synthetic activity related to polypyrroles [216-218], Reviews are available on various aspects of the synthesis and properties of polypyrroles [219,220]. In addition, summaries of important aspects of polypyrroles are included in several reviews on electrically conducting polymers [221-226]. Polypyrrole has been synthesized by chemical polymerization in solution [227-231], chemical vapor deposition (CVD) [232,233], and electrochemical polymerization [234-240]. The polymer structure consists primarily of units derived from the coupling of the pyrrole monomer at the 2,5-positions [Eq. (84)]. However, up to a third of the pyrrole rings in electrochemically prepared polypyrrole are not coupled in this manner [241]. 

In this application, the conducting polymer serves as the chemically-sensitive film that transduces an immunoassay into an electrical signal. A major advantage in using conducting polymers for immunoassay-based biosensors (immunosensors) is that antibodies can be coated directly onto the active polymer surface with little degradation of antibody functionality. 

In three-dimensional mixed-valence systems, electron transfer can manifest itself as electrical conduction, thermally activated. Most work continues to focus on the better known semiconducting materials such as silicon-boron or silicon nitride " (at low temperature), or organic crystals of the anthracene type (at high temperature),or redox polymer-coated electrodes. In the last-mentioned case, the importance of ion migration as well as electron transfer has recently been emphasized. In the mixed-valent Tl(I)3Tl(III)Cl6, conductivity and isotopic exchange studies have been taken to indicate that cation transfer is the principal charge-carrying mechanism, and not electron transfer as such. " Mossbauer... 

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