Aerosol Jet Printing of Phase-Inversion Graphene Inks for High-Aspect-Ratio Printed Electronics and Sensors

Aerosol jet printing is a technology particularly suited for additive manufacturing of functional microstructures, offering resolutions as high as 10 μm, broad compatibility for electronic nanomaterials, and noncontact deposition, making it compelling for device prototyping and conformal printing. To adapt this method from thin film patterns to taller features, both ink rheology and drying kinetics require careful engineering. Printing in a solvent-rich, low-viscosity state commonly results in a puddle, with liquid-phase spreading and susceptibility to instabilities, whereas printing solvent-depleted aerosol results in a granular morphology with high overspray. Here, we demonstrate a strategy to mitigate this trade-off by tailoring the evolution of ink rheology during the process, using a graphene ink containing the nonsolvent glycerol as an exemplar. During droplet transport to the nozzle, evaporation of volatile primary solvents increases the glycerol concentration, resulting in gel formation. This switch in the ink rheology between the cartridge and substrate maintains the print resolution at high deposition rates. Moreover, multiple layers can be printed in rapid succession to build up high aspect ratio microstructures, as demonstrated by continuously printed cylindrical pillars with diameters on the order of ∼100 μm and aspect ratios as high as ∼10. Finally, the efficacy of this ink formulation strategy for a CuO nanoparticle ink confirms the generalizability of this strategy for a broader scope of colloidal nanomaterial inks. In addition to its utility for microscale additive manufacturing of 2.5D structures, this strategy provides insights into higher deposition rate patterning to improve scalability and throughput of aerosol jet printing.