Polyaniline

Polyaniline (PANI) is a conducting polymer produced by oxidative polymerization of aniline. Its electrical conductivity can be turned on or off by oxidation level and protonic acid doping. It is notable for environmental stability and ease of processing into films, fibers, and dispersions.

As a polymer, polyaniline consists of repeating aniline units linked through C–N backbones. It exists in several oxidation states: leucoemeraldine (fully reduced), emeraldine (half-oxidized) and pernigraniline (fully oxidized). The conductive form is emeraldine when protonated, forming emeraldine salt; emeraldine base is insulating.

Synthesis commonly involves chemical oxidative polymerization of aniline in acidic aqueous solution using an oxidant such as ammonium persulfate or iron(III) chloride. The material can be subsequently dedoped to the base form. Conductivity is enhanced by protonic acid dopants such as hydrochloric acid or camphor sulfonic acid, and by processing conditions.

Polyaniline features moderate to high environmental stability, and its conductivity can be tuned over several orders of magnitude depending on oxidation and doping. It forms films, fibers, nanostructures, and composites, and shows electrochromic color changes associated with redox state and doping level.

Applications include antistatic coatings, electrochromic displays, energy storage devices (supercapacitors and batteries), chemical and biological sensors, and corrosion-resistant coatings. Polyaniline's discovery in the 1980s by researchers including MacDiarmid, Heeger, and Shirakawa led to the Nobel Prize in Chemistry in 2000.