Printable, porous, electrically conductive composite via in situ non-solvent-induced phase separation

Digital printing of porous conductive inks is essential for circuit applications that require the printed traces to have a high surface area. Here, we introduce a method for direct ink writing (DIW) of porosity-tunable conductive inks that is free of post-processing steps. This is accomplished using an in situ non-solvent-induced phase separation mechanism in which silver flakes, eutectic gallium-indium droplets, and carbon nanotubes are suspended within a ternary phase solution of polycaprolactone, toluene, and dimethylformamide. The resulting ink has an adjustable electrical conductivity spanning 103–105 S/m and can achieve a tunable porosity of 5%–21% with a pore size range of 1–12 μm. By integrating the in situ phase separation mechanism into DIW, we can combine micrometer-scale phase-separated pores with sub-millimeter-scale printed pores to achieve multi-scale porosity. This conductive ink formulation demonstrates a way to directly tune material properties with printing, which has the potential to extend to other compositions to enable practical applications.