Electrical properties polypyrrole conductivity

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]. 

All experiments showed that the corresponding polymers precipitated from solution. After filtration and washing with hot water, polypyrrole and poly(EDT) were obtained as dark powders in their oxidized state. Conductivity measurements showed that these materials have the same electrical properties (10-100 S cur1) as conventionally prepared polypyrrole or poly(EDT) [27,28],... 

Another interesting application that uses the dynamic properties of conducting polymers is electrochromic devices.44,45 46 47 An electrochromic device based on polypyrrole is shown in Figure 1.8. The polypyrrole changes from colorless to black when it is oxidized by the application of positive potentials. Similarly, polythiophene and polyaniline undergo distinct color changes when an electrical potential is applied. 

Polypyrroles (PPy s) are formed by the oxidation of pyrrole or substituted pyrrole monomers. In the vast majority of cases, these oxidations have been carried out by either (1) electropolymerization at a conductive substrate (electrode) through the application of an external potential or (2) chemical polymerization in solution by the use of a chemical oxidant. Photochemically initiated and enzyme-catalyzed polymerization routes have also been described but are less developed. These various approaches produce polypyrrole (PPy) materials with different forms—chemical oxidations generally produce powders, whereas electrochemical synthesis leads to films deposited on the working electrode, and enzymatic polymerization gives aqueous dispersions. The conducting polymer products also possess different chemical/electrical properties. These alternative routes to PPy s are therefore discussed separately in this chapter. 

R.A. Zoppi, at the Chemistry Institute of Campinas State University, performed a series of experiments on the S5mthesis of polypjrrrole in an EPDM rubber matrix, under the supervision of Professors M.A. de PaoH and M.I. Felisberti. The objective of the study was to obtain a product with electrical properties similar to those of polypyrrole and mechanical properties like those of EPDM rubber. Pol rpyrrole, a conducting polymer, is very brittle, which prevents its use in apphcations of practical interest. 

H.J. Lee and S.M. Park, Electrochemistry of conductive polymers 37. Nanoscale monitoring of electrical properties during electrochemical growth of polypyrrole and its aging. J. Phys. Chem. B, 109, 13247 (2005). 

Y. Long, Z. Chen, X. Zhang, J. Zhang, and Z. Liu, Electrical properties of multi-walled carbon nanotube/polypyrrole nanocables percolation-dominated conductivity, J. Phys. D Appl. Phys., 37, 1965 1970 (2004). 

PROPERTIES OF SPECIAL INTEREST presence of an extended 7r-bonding system, which imparts electrical properties to the polymer. Doping either p or m can enhance these properties. Polypyrrole is stable in air at room temperature as well as at temperatures as high as 250°C in its doped state. Also, polypyrrole can be synthesized in a doped state. It changes color when switched from its conducting to insulating state. 

FIGURE 16.4 I-V characteristics of iodine doped PA nanofiber. Znsef shows scanning force microscope image of PA nanofiber on top of Pt electrodes (with 100 nm separation). Typical diameter of PA nanofiber is 16-20 mn (From Park, J.G., et al. Synth. Met., 119, 53, 2001 and Park, J.G., Electrical transport properties of conducting polymer nanostructures Polyacetylene nanofiber, polypyrrole nanotube/nanowire, Ph.D. thesis, Seoul National University, Seoul, 2003.). 

Park, J.G. 2003. Electrical transport properties of conducting polymer nanostructures Polyacetylene nanofiber, polypyrrole nanotube/nanowire. Ph.D. thesis, Seoul National University, Seoul. 

Satoh, M., Kaneto, K., and Yoshino, K., Dependences of electrical and mechanical properties of conducting polypyrrole films on conditions of electrochemical polymerization in an aqueous media, Synth. Met., 14, 289-296 (1986). 

Ansari, R., and Wallace, G. G., Effect of thermal treatment on the electrochemical properties of conducting polypyrrole polymers. Polymer, 35, 2372-2377 (1994). Samuelson, L. A., and Druy, M. A., Kinetics of the degradation of electrical conductivity in polypyrrole. Macromolecules, 19, 824-828 (1986). 

The experimental conditions of preparation deeply affect the electrical properties of the final material. A polypyrrole sample with a conductivity of 328 S cm has been obtained by careful control of the oxidation potential in a binary solution of acetonitrile and methanol [88]. Different chemical characteristics of poly pyrrole are obtained by varying the initial concentrations of Fe " and pyrrole in the polymerization solution [89]. Polypyrrole obtained by chemical oxidation is usually in the form of a black powder. Freestanding poly pyrrole films were prepared at room... 

Aleshin, A. N., Mironkov, N. B., Suvorov, A. V., Conklin, J. A., Su, T. M., and Kaner, R. B., Electrical properties of ion implanted and chemically doped polyaniline films, in Materials Research Society Symposium Proceedings on Electrical, Optical and Magnetic Properties of Organic Solid State Materials III, Vol. 413, 1996, p. 609. Cameron, D. A., and Reynolds, J, R., Conducting molecular composites of polypyrrole with electroactive polymeric dopant ions, ACS Proc., 37, 684 (1996). 

The redox properties of conducting heterocyclic polymers like polypyrrole are central to many applications of these materials. For this reason the electrochemistry of thin films of these polymers have received a lot of attention. For use in electrically controlled ion binding and delivery, the general idea is that the heterocyclic conducting polymers have cationic backbones and will incorporate counter anions. Upon reduction of the backbone, the anions will be flushed out. Thus, in principle one can develop devices to absorb anions of interest or to release them in response to an electric current. Our work has been spurred by the possibility of delivering drugs with a rate controlled by the current. 

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