Conducting Polymers and Their Applications

kedi (63)in #science • 7 years ago (edited)

Polymers are known as good electrical insulation materials, and due to these properties, they are important in areas where electrical insulation is required. Other important advantages are their easy handling, flexibility, aesthetic appearance, lightness and chemical inertness.

Polymer applications in the industry have expanded with studies on the superior mechanical properties of polymers and the incorporation of conductive properties. In 1977 Shirakawa and his colleagues opened a new door for the technological development of polymers, with the idea that a polymer with conjugate bonding can be collected by iodine and acquire conductive properties. Since then, studies on conductive polymers have increased and many materials made using such polymers have been commercialized.

Electroactive conducting polymers exhibit electrical and optical properties previously found only in inorganic systems. Conducting polymers differ from inorganic crystalline semiconductors such as silicon in terms of their molecular structure. Due to their conjugated π-electron skeleton, conductive polymers possess electronic properties such as electrical conductivity, low-energy optical transition, low ionization potential and high electron mobility. These materials with high conductivity are also called synthetic metals.

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Structure of some conducting polymers

One of the accepted approaches in the literature for low band-gap polymer synthesis is the Donor-Acceptor Theory. According to this theory, the coexistence of donor and acceptor groups within a conjugate chain provides a shift in the valency and conductivity bands and the synthesis of materials with lower band spacing is possible.

Conductive polymers have recently attracted considerable attention, especially in the field of electrochemistry. The first important study of conductive polymers in the foreground was made in the 1970's and it was thought that polyacetylene film could be used as conductive material by determining that it exhibits metallic properties by adding some materials. Since its first discoveries, conductive polymers have found application in industrial areas such as electrochromic devices, light emitting diodes, sensors and organic solar cells.

One of the important application fields of conductive polymers is electrochromic devices. There is a reversible color change which can be observed depending on the applied tension in these devices. This is named as electrochromism. The color change of the polymer can take place between the transparent state and the colored state or between two different colors. The polymers with more redox region show multi-chromatic properties.

Electrochromic device stack schematic, depicted in a darkened state.

Many studies have been carried out on inorganic materials and electrochromic devices made of these materials. However, such inorganic electrochromic materials are expensive and have some problems such as not being able to obtain any kind of color. Polymeric materials are less stable and it is possible to achieve color diversity with the changes that can be made in the structures. The use of conductive polymers as an active layer in electrochromic devices has become more popular due to the advantages such as fast switching times, high optical contrast, ease of processing and easy adjustment of the band gap. Electrochromic materials have many technological applications such as rear view mirrors, intelligent glasses that provide solar control, optical screens, camouflage materials.

In parallel with the development of science and technology, organic solar cells, an important application area of organic electronic materials, will continue to be widely used in the following years. This technology is effective electron transfer between the basic electron acceptor and electron donor molecules. Since the soluble conductive polymers can be coated on large surfaces, it can be produced at low cost and easy to produce, the field of application can be found in solar batteries and the researchers on this subject are still going on.

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