Stretchable and flexible PEDOT:PSS/SWCNTs/PEO film with strain-insensitive electrical resistance

The poly-(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS), single-walled carbon nanotubes (SWCNTs), and polyethylene glycol (PEO) were composited and subsequently spin-coated on a Polydimethylsiloxane (PDMS) substrate to prepare a stretchable and flexible bilayer film, and the electrical resistance of the film was adjusted to be unchanged by the pre-stretching processing. The interpenetrating structure was formed within the PEDOT:PSS/SWCNTs/PEO film when the PEO concentration was 5 wt%. The PEDOT:PSS and SWCNTs served as the electric phase forming the conductive path, while the PEO acted as the elastic phase, thereby enabling the film to exhibit stretchability, flexibility, and high conductivity. The pre-stretching processing, which consisted of sequential uniaxial stretching and relaxation, resulted in wrinkling of the PEDOT:PSS/SWCNTs/PEO film due to the stretching strain exceeding the elastic deformation limit. The transmittance changes of the films subjected to the pre-stretching processing also proved that the wrinkles were formed. The film, comprising 5 wt% PEO and 10 wt% SWCNTs, exhibited a minimum sheet resistance of 43 Omega/sq. without pre-stretching and demonstrated stable electrical resistance when subjected to pre-stretching processing with 50% strain. The bilayer film with pre-stretching processing had achieved a comparable level of performance to that of contemporary medical electrodes for electrocardiogram detection. Meanwhile, the bilayer film without pre-stretching could be utilized as a strain sensor for monitoring body motion.