Electrical conductivity, 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). 

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... 

Furthermore, porous CPs (e.g., polypyrrole, polyanUine) films have been used as host matrices for polyelectrolyte capsules developed from composite material, which can combine electric conductivity of the polymer with controlled permeability of polyelectrolyte shell to form controllable micro- and nanocontainers. A recent example was reported by D.G. Schchukin and his co-workers [21]. They introduced a novel application of polyelectrolyte microcapsules as microcontainers with a electrochemically reversible flux of redox-active materials into and out of the capsule volume. Incorporation of the capsules inside a polypyrrole (PPy) film resulted in a new composite electrode. This electrode combined the electrocatalytic and conducting properties of the PPy with the storage and release properties of the capsules, and if loaded with electrochemical fuels, this film possessed electrochemically controlled switching between open and closed states of the capsule shell. This approach could also be of practical interest for chemically rechargeable batteries or fuel cells operating on an absolutely new concept. However, in this case, PPy was just utilized as support for the polyelectrolyte microcapsules. 

Besides the intrinsic conductive polymers, some deformable polymers, such as shape-memory polymers, are usually activated by heating. After incorporating with conductive fillers, such as carbon nanomaterials, they can be simulated by the electricity through Joule heating (Liu et al., 2009 Hu and Chen, 2010 Koerner et al., 2004). This kind of electro thermally active polymer composites can produce expansion/contraction and bending behaviors upon with the electricity. Moreover, these actuators can work durably... 

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