Conductive Electroactive Polymers structure

Conducting electroactive polymers (CEPs) such as polypyrrole, poly thiophene, polyaniline, and sulfonated polyaniline (1-4 shown subsequently) are complex, dynamic structures that captivate the imagination of those of us involved in intelligent material research.1 2 3 4 5... 

PAn is now accepted to have the general polymeric structure shown as 1. It differs from most other conducting electroactive polymers, such as polypyrroles (PPy s Chapters 2 and 3) and polythiophenes (Chapter 6), in that it possesses three readily accessible oxidation states. These range from the fully reduced (y = 1) leucoemeraldine state to the half-oxidized (y = 0.5) emeraldine form to the fully oxidized (y = 0) pernigraniline state. The ES form 2 is the state with the highest conductivity. 

This ability to pattern in three or two dimensions is critical to the development of intelligent material structures containing conducting electroactive polymers. Advances in patterning are described in the following section. 

Rapid advances in synthetic polymer science and nanotechnology have now placed us in a position to utilize the unique properties of this versatile class of materials. Our ability to design and assemble polymers from the molecular level, coupled with a better understanding of structure-property relationships enables the design of sophisticated structures. We believe that inherently conducting electroactive polymers (CEPs) will continue to play a central role in the development of intelligent material science over the following decades. 

Conducting electroactive polymers contain functional groups (—NH—, —S—) that make the direct complexation of metals possible. For example, copper ions are readily complexed by polypyrrole to yield the following structure [142] ... 

A. Mirmosheni, W. E. Price, and G. G. Wallace, Adaptive membrane systems based on conductive electroactive polymers. Journal of Intelligent Material Systems and Structures 4(1) 43 (1993). 

A Structural characteristic of conducting organic polymers is the conjugation of the chain-linked electroactive monomeric units, i.e. the monomers interact via a 7t-electron system. In this respect they are fundamentally different from redox polymers. Although redox polymers also contain electroactive groups, the polymer backbone is not conjugated. Consequently, and irrespective of their charge state, redox polymers are nonconductors. Their importance for electrochemistry lies mainly in their use as materials for modified el trodes. Redox polymers have been discussed in depth in the literature and will not be included in this review. 

In considering the potential applications of electroactive polymers, the question always arises as to their stability. The deterioration of a physical property such as conductivity can be easily measured, but the chemical processes underlying it are not as easy to be revealed. In order to understand them, XPS has been used to follow the structural changes which occur in the polymer chain and the counter-ions of the doped polymer. The following sections present some XPS findings on the degradation of electroactive polymers, such as polyacetylene, polypyrrole, polythiophene and polyaniline, in the undoped and doped states. 

As intensive studies on the ECPs have been carried out for almost 30 years, a vast knowledge of the methods of preparation and the physico-chemical properties of these materials has accumulated [5-17]. The electrochemistry ofthe ECPs has been systematically and repeatedly reviewed, covering many different and important topics such as electrosynthesis, the elucidation of mechanisms and kinetics of the doping processes in ECPs, the establishment and utilization of structure-property relationships, as well as a great variety of their applications as novel electrochemical systems, and so forth [18-23]. In this chapter, a classification is proposed for electroactive polymers and ion-insertion inorganic hosts, emphasizing the unique feature of ECPs as mixed electronic-ionic conductors. The analysis of thermodynamic and kinetic properties of ECP electrodes presented here is based on a combined consideration of the potential-dependent differential capacitance of the electrode, chemical diffusion coefficients, and the partial conductivities of related electronic and ionic charge carriers. 

In the development and fabrication of molecular-based electronics, it is essential to have a good understanding of the chemistry and electronic struemre of the electroactive polymer interface with other polymers, semi-conductors and metals. A better understanding of the CT interactions at the polymer/metal interface will also facilitate the application of conductive polymer coatings for metal passivation and corrosion prevention [268]. An overview of measurement methods and quantum chemical calculation techniques for smdying the chemical and electronic structure of conjugated... 

Through a comprehensive review of the recent conductive polymer literature, it has been demonstrated that photoelectron spectroscopy provides a very unique and powerful tool for analyzing the intrinsic structure, the charge transfer interaction, and the stability and degradation behaviour of electroactive polymers. It is further demonstrated that photoelectron spectroscopy is also ideal for investigating the chemistry and electronic structure of the electroactive polymer interface with other polymers, semi-conductors, and metals. The surface and interfacial analytical capability of photoelectron spectroscopy can be further extended to include molecular specificity when coupled with the SIMS technique. Finally, the imaging XPS technique is fast becoming widely available [368]. 

Madden, J.D.W., P.G.A. Madden, and I.W. Hunter. 2002. Conducting polymer actuators as engineering materials. Presented at the Proceedings of the SPIEs 9th International Symposium on Smart Structural Materials, Electroactive Polymer Actuators and Devices (EAPAD), San Diego, CA. 

Otero, T.F., M.T. Cortes, I. Boyano, and G. Vazquez. Non-stoiquiometry and tactile muscles with conducting polymers. Proceeding of SPIE, Smart structures and materials 2000 Electroactive Polymer Actuators and Devices 5385(2004) 425-432. Ed. Y. Bar-Cohen. 

Mazzoldi, A. and De Rossi, D. (2000). Conductive-polymer-based structures for a steerable catheter, in Y. Bar-Cohen (ed.), Smart Structures and Materials 2000 Electroactive Polymer Actuators and Devices (SPIE - The International Society for Optical Engineering, Bellingham, WA), pp. 273-280. 

Jung YC, Goo NS, Cho JW (2004) Electrically conducting shape memory polymer composites for electroactive actuator. In Bar-Chen Y (ed) Proceedings of the SPIE 5385 Smart structures and materials 2004 Electroactive polymer actuators and devices. International Society for Optics and Photonics, Bellingham, doi 10.1117/12.540228... 

Evidently, conducting polymers with an ordered structure have the advantage of a combination of high conductivity with good solubility properties. The alkylated electroactive polymers such as poly(3-alkylthiophene)s and N-alkylated polyanilines can be compared with alkylated liquid crystalline polyesters and polyamides. 

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