Extrinsically conductive polymers

Extrinsic conductive polymers obtained by adding specific additives to naturally insulating polymers. At present, this is the easiest industrial method. 

Polyanitine was the first CP polymer, which was described in the mid-19th century by Henry Letheby [36]. Since then numerous intrinsically CP have been developed, among others polyacetylene, polythiophene, polypyrrole. CPs, also referred to as synthetic metals, have found applications in many fields. They are integrated for example in solar cells, rechargeable batteries and biomedical devices [37]. CPs are also very attractive for biosensors. In biosensors, CP can be used as excellent non-metallic electrodes. Numerous biosensors have been developed over the past 20 years with electrodes made of CP. The fabrication is fairly easy and flexible. This allows the biosensors to be single-use system avoiding any risk of contamination and adaptation of the biosensors to new targets can be rapidly made. They are mostly biocompatible, can easily be synthesized and can be modified for immobilization of bioelements [38]. These conductive polymers are referred to as intrinsic conductive polymers in comparison to extrinsic conductive polymers that are a polymer matrix in which some metal particles have been entrapped [39]. 

There are two distinct types of stability. Extrinsic stability is related to vulnerability to external environmental agent such as oxygen, water, peroxides. This is determined by the polymers susceptibility of charged sites to attack by nucleophiles, electrophiles and free radicals. If a conducting polymer is extrinsic unstable then it must be protected by a stable coating. 

Recent work has investigated conductive polymers [69,70], sol-gels [71], and chemoresponsive dyes [72] for use as the gas-sensitive transduction medium in fiber optic sensors. In general, fiber optic sensors can be divided into two different sensing architectures extrinsic and intrinsic. If the transduction of the chemical signal into an optical signal occurs within the fiber... 

Polythiophenes in the neutral state are stable in the dark under atmospheric conditions but the conductivity of doped polythiophene and poly(3-alkylthiophene)s decreases rapidly. This lack of stability is one of the major barriers to industrial application of polythiophenes as conductive materials. Extrinsic and intrinsic factors determine the stability of a conductive polymer. Extrinsic instability is mainly due to the reaction of the charged defects with water vapor and oxygen. A... 

Whether this model is true in "real" polymers is still an open question. Nevertheless, BPs must appear in conducting polymers upon heavily doping, regardless of whether or not Eq. (8) is exothermic. When heavily doped, however, another type of charge excitation can be formed an extrinsic bipolaron (as opposed to an intrinsic BP), or 77 dimer (PD- ), in which two polarons at different chains are coupled. The PD excitations are spinless (Fig. 22.3c), and therefore their formation has been recently proposed to explain the dramatic decrease in unpaired spins observed in FeCb-doped a-sexithio-phene at low temperatures [32]. Then the possibility that PD charge excitations can be photogenerated cannot be discarded. 

All conjugated polymers (CPs) are semiconductors with wide forbidden gaps, generally on the order of 2 eV or more. Some have a low conductivity of extrinsic origin, others are insulators. They become conductors by injection of electrons or holes onto the chains, with simultaneous intercalation of compensating ions between the chains. This is the so-called... 

Doped polyacetylene conducts electrons via an intrinsic mechanism rather than by an extrinsic one. That is to say, conductivity of the polymer is due directly to electronic conductivity rather than to charge carrier motion. 

The detection of chemical analytes can be based on changes in one or more of physical characteristics of thin film or layer in contact with the device surface. Some of the intrinsic film properties that can be utilized for detection include mass/area, elastic stiffness (modulus) viscoelasticity, viscosity electrical conductivity, and permittivity. In addition, changes in extrinsic variables such as temperature and pressure also produce a sensor response [31, 32]. SAW sensor works as a mass sensor, when analytes of interest comes in contact of polymer film, which is coated, on SAW device. Desired toxic gas is exposed to the device through the carrier gas such as Na and then gas molecules are desorbed [5, 33, 34]. Device has been tested for determining the characteristics such as (i) frequency shift with different concentration of vapor (ii) transient response for response and recovery times (iii) transient response for reproducibility of the sensor. Since arrangement has been made to compensate the... 

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