Extremely-fast electrostatically-assisted direct ink writing of 2D, 2.5D and 3D functional traces of conducting polymer Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate- polyethylene oxide (PEDOT:PSS-PEO)

Hypothesis: Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is an attractive conducting polymer, albeit its rheological properties are inappropriate for direct ink writing (DIW). Here it is hypothesized that a suspension of PEDOT:PSS with a non-conducting highly spinnable viscoelastic polymer, e.g., polyethylene oxide (PEO), will significantly facilitate printability and enhance the electrical conductivity (EC) of PEDOT:PSS-PEO. It is also hypothesized that high-humidity post-treatment will enhance the EC even further, and the application of the electric field can facilitate the DIW speed beyond the capabilities of current commercial 3D printers. Experiments: The rheological behavior of PEDOT:PSS suspensions with several non-conducting polymers was explored in the experiments. The EC of the suspensions was measured, including the effect of high-humidity post-treatment. High-speed DIW of the optimal suspension was experimentally demonstrated with the applied electric field. Findings: The findings revealed that PEO serves as a secondary dopant, and the suspension of 4.33 wt% PEDOT:PSS-52 wt% PEO possesses the EC > 15 times higher than that of PEDOT:PSS. Many 2D, 2.5D and 3D functional traces were printed at high resolution at the DIW speed up to 8.64 m/s (>10 times faster than current commercial printers), facilitated by the applied electric field. Post-treatment at 80–90% relative humidity enhanced the EC more than twice.