Poly(3,4-ethylenedioxythiophene):Poly(styrene sulfonate) Inkjet Inks Doped with Carbon Nanotubes and a Polar Solvent: The Effect of Formulation and Adhesion on Conductivity

A conductive aqueous polymer suspension of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), or PEDOT:PSS, was used as the basis for an inkjet-printable and translucent conductive material. Several types of surfactants were used to achieve suitable particle sizes for inkjet printing, with Zonyl™ FS-300 non-ionic surfactant providing suitable surface tension, stability and dispersion. Viscosity was controlled using water and glycerol. Glycerol was also included as a humectant. 10 w/w% polar solvent (dimethyl sulfoxide) was used to increase conductivity, as a co-solvent and as a viscosity modifier. Carbon nanotubes, both single- and multi-walled, were dispersed in the ink to further improve its conductivity. The optimized ink was printed onto coated photo-paper and cellulose acetate (CA) substrates and characterized for ink layer thickness and conductivity. The effect of paper folding and peeling of an adhesive strip from the ink surface on the conductivity of the printed samples was also characterized. Optical microscopy showed that the conductive ink was contained almost entirely in the pores of the photo-paper coating layer and fibres, but remained as a film on the CA surface. In the case of photo-paper, failure occurred primarily at the coating–paper interface. The cohesive failure compromised the conductivity of the PEDOT:PSS layer contained in the coating. In the case of CA (within the coating layer), the PEDOT:PSS film's conductivity was not significantly affected by folding or peeling. This suggests that PEDOT:PSS is a robust conductive material well-suited to applications requiring significant flexibility.