Salt-induced ductilization and strain-insensitive resistance of an intrinsically conducting polymer

High mechanical ductility and high mechanical strength are important for materials including polymers. Current methods to increase the ductility of polymers such as plasticization always cause a remarkable drop in the ultimate tensile strength. There is no report on the ductilization of polymers that can notably increase the elongation at break while not lowering the ultimate tensile strength. Here, we report the salt-induced ductilization of an intrinsically conducting polymer, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS). Treating highly conductive PEDOT:PSS with a salt such as sodium perchlorate can enhance its elongation at break from 8.5 to 53.2%, whereas it hardly affects the tensile strength. Moreover, the resistance of the ductilized PEDOT:PSS films is insensitive to the tensile strain before fracture and slightly increases by only ~6% during the cyclic tensile testing with the strain up to 30%. These effects are ascribed to the decrease in the Coulomb attraction between PEDOT⁺ and PSS^- by the salt ions.