Thin-film fabrication and electrochemical characterization of PEDOT:carrageenan composites

  We synthesized conductive thin films of poly(3,4-ethylenedioxythiophene) (PEDOT):carrageenan composites to explore how the number of ester sulfate groups from one to three per disaccharide repeating unit in carrageenan affect the electrochemical properties of the composites, as an effort to search for sustainable organic mixed ionic-electronic conductors (OMIECs). We employed a spray-coating method to fabrication the composite films, because of their gelling nature of carrageenan. To study their electrical, electronic, and electrochemical properties, we used four-point probe DC conductivity measurements, UV-vis-NIR spectroscopy, spectroelectrochemistry (SPE), and electrochemical impedance spectroscopy (EIS). PEDOT:κ-carrageenan (one sulfate per disaccharide) exhibited the highest NIR absorption bands from the doped states, corresponding to the highest conductivity (~2.5 S/cm) among the three systems. Substantial electrochemical switching of absorbance (Δα) was also observed from PEDOT:κ-carrageenan, whereas the systems with two (ι) and three (λ) sulfate groups per disaccharide showed negligible electrochemical responses. This work necessitates further mechanistic studies to clarify how sulfate density and the macromolecular architecture synergistically modulate interactions with π-conjugated polymers.