Applications of Conducting Polymers

Abstract

For practical reasons, electronically conducting polymers that can be prepared from cheap compounds such as aniline, pyrrole, thiophene and their derivatives by relatively simple chemical or electrochemical polymerization processes attract the most interest. However, redox polymers are also applied in special cases, such as in biosensors or electrochromic display devices. Nevertheless, in this chapter we focus our attention on the applications of electronically (intrinsically) conducting polymers, which we will refer to as "conducting polymers," or by the abbreviations "ECPs" and "ICPs." The most interesting property of conducting polymers is their high (almost metallic) conductivity, which can be changed by simple oxidation or reduction, and also by bringing the material into contact with different compounds. Conducting polymers usually have good corrosion stabilities when in contact with solution or/and in the dry state. For instance, polyaniline is stable in its leucoemeraldine and emeraldine states, even in 10 mol dm −3 acid solutions. Furthermore, ICPs can be deposited from a liquid phase, even in complex topographies. Redox processes combined with the intercalation of anions or cations can therefore be used to switch the chemical, optical, electrical, magnetic, mechanic and ionic properties of such polymers. These properties can be modified by varying the anion size and preparation techniques; by including other chemical species for example. A qualitative summary of the relationship between the properties of a conducting polymer and its charge state is given in Table 7.1.Typical areas in which conducting polymers are applied can be described using a double logarithmic plot of ionic resistance versus electronic resistance, as shown in Fig. 7.1.The positions of ideal metals, semiconductors and insulators in the diagram are shown at the top. Constant properties exist at high ionic resistances, i.e., towards the top of the diagram. Here, ICPs can be applied in the dry state in an inert atmosphere. Contact with an electrolyte leads to a much wider field of applications, depending on the specific ionic and electronic resistances associated with the charge state, such as in batteries, displays, sensors, etc.