PEDOT:PSS as Stretchable Conductors with Good Wettability on the Substrate through the Simultaneous Plasticization and Secondary Doping with a Cationic or Anionic Surfactant

Stretchable conductors are indispensable units of stretchable/wearable electronic devices and systems. However, the conventional conductors including metals, semiconductors, intrinsically conducting polymers, carbon nanotubes, and graphene have very limited mechanical stretchability. It is thus significant to develop stretchable conductors. Here, cationic and anionic surfactants are studied to plasticize poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) that is the most successful conducting polymer in terms of practical application for the first time. Apart from the increase in the mechanical stretchability of PEDOT:PSS, these ionic surfactants can also enhance the conductivity via secondary doping and improve the wettability on the substrate simultaneously. The cationic surfactants can increase the elongation at break of PEDOT:PSS to >50%, higher than that (≤41%) of the anionic surfactants. The different plasticization effects are ascribed to their different interactions with PEDOT:PSS. The amphiphilic cations of a cationic surfactant can associate with the negatively charged PSS– chains, thereby lowering the Coulomb attraction between PEDOT+ and PSS– chains. This can increase the freedom of the polymer chains and cause the disappearance of the hydrogen bonds among PSS(H) chains or segments. Instead, the amphiphilic anions of an anionic surfactant can substitute PSS– as the counter anions of PEDOT+, thereby increasing the freedom of the polymer chains and induce the conformational change of the PEDOT+ chains. In addition, both the cationic and anionic surfactants can enhance the conductivity of PEDOT:PSS films to about 400 S cm–1. This is ascribed to the secondary doping by these surfactants by inducing the phase segregation and conformational change of PEDOT. Hence, the PEDOT:PSS films blended with a cationic or anionic surfactant can have high mechanical stretchability and high conductivity. In addition, the ionic surfactants can greatly improve the wettability of the PEDOT:PSS solution on a hydrophobic substrate.