| Conducting Polymers |
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Polymers are typically thought of in terms of the commercial plastic products used daily. These plastics are insulating materials and are not used directly in electrical, antistatic or electromagnetic shielding applications. Conductive fillers can be added to add additional physical properties such as electrical conductivity. The choices for conductive fillers are typically inorganic materials such as metals, metal oxides, inorganic compounds, carbon black, carbon nanotubes or other carbon allotropes. Most of these choices are expensive, difficult to process and disperse poorly into commercial plastics. These additives may also have negative impact on mechanical properties due to their different thermal expansion rates and flexibility. Inherently conducting polymers (ICPs) are polymers that have an intrinsic ability to conduct electricity. These include polyacetylene, polypyrroles, polythiophenes and polyanilines among others. With an appropriate dopant and the appropriate oxidation state these polymers generate polarons or bipolarons which allow conduction of electrons along the pi-orbitals of the conjugated polymer backbone. Polyaniline is unique among ICPs because its native oxidation state, emeraldine is appropriate for electron conduction, and the presence or absence of a protonic dopant is sufficient to switch it from a conductive to an insulating state. Polypyrroles and polythiophenes are doped by changing the oxidation state of the polymer. The “dopant” in conducting polymers is the agent that adds or removes electron density to the polymer chain, depending on the ICP. A counter-ion stabilizes the charge on the backbone and can be confused with the dopant. In the case of polyaniline a proton is the dopant, while the counterion stabilizes the charge. Conventional micron structured conducting polymers are processable in a limited number of solvents, and can be difficult to solubilize. Nanostructures are easily processable because their large surface charge to volume ratio provides stability, in solvents, particularly in water. Other suppliers of conducting polymers use surfactants, stabilizers or emulsion polymerization techniques (which require organic solvents and/or organic dopants), which are more energy intensive and generate more waste than Fibron Technology's efficient all-aqueous synthesis and processing. The water processing methods of polyaniline nanofibers are much more environmentally friendly than conventional organic processing. Nanofibers provide additional benefit because less material is required to create a conducting pathway to percolate through a coating or as an additive in a polymer composite. Because conducting polymers are more similar structurally to conventional polymers, they have similar expansion coefficients, diffraction coefficients, densities and mechanical properties, beneficial in plastic composites. Fibron’s nanofibers are also dispersable in many solvents, including alcohols, acetone and others and can be dissolved in conventional polyaniline solvents, such as N-methylpyrrolidinone and meta-cresol. |