Polyanilin

Polyaniline, often abbreviated PANI, is a conducting polymer built from repeating aniline units linked through carbon–nitrogen bonds. It exhibits several oxidation states, notably leucoemeraldine (fully reduced), emeraldine (half-oxidized), and pernigraniline (fully oxidized). The conductive form is the emeraldine salt, produced when the emeraldine base is doped with protonic acids. In its base form, polyaniline is generally insulating, while protonic acid doping introduces charge carriers that raise its electrical conductivity.

Synthesis of polyaniline typically involves oxidative polymerization of aniline in strongly acidic aqueous media using oxidants such as ammonium persulfate. The reaction is conducted at low temperatures to favor polymer formation. The resulting emeraldine base can be converted to the emeraldine salt by treatment with acids like hydrochloric, sulfuric, or camphorsulfonic acid. Polyaniline preparation can yield various molecular weights and morphologies, including powders, fibers, and films.

Properties of polyaniline include relatively good environmental and thermal stability for a conducting polymer, and a wide tunable range of electrical conductivity depending on oxidation state and dopant (from insulating to conductive, typically spanning several orders of magnitude). The polymer is largely insoluble in most common organic solvents but can be processed in doped forms as dispersions or films. Doping also affects optical properties and conductivity, enabling electrochromic behavior in some forms.

Applications are diverse and include antistatic coatings, electromagnetic interference shielding, corrosion protection, chemical sensing, and energy storage devices such as supercapacitors and battery electrodes. Polyaniline’s easy synthesis, environmental stability, and tunable conductivity have kept it a prominent material in research and applied electronics.