Theoretical and experimental studies of electrostatic focusing for electrohydrodynamic jet printing

Electrohydrodynamic jet (e-jet) printing technology has the capability of sub-micrometer resolution with large-range viscous inks, but is incompatible with nonplanar and insulating substrates. Here, we develop a theoretical model for an electrostatic lens that is incorporated into an e-jet system to shape the electric field inside the printhead. The electrostatic lens can generate electrostatic focusing to drive a Taylor cone for the generation of jetting, without a voltage being applied between the printhead and the substrate, which avoids the influence of standoff height on the nonplanar substrate and the charge repulsion from polarization of the insulating substrate. The theoretical model, in combination with finite element simulation, is established to reasonably calculate each design parameter of the electrostatic lens-integrated printhead. Further, the e-jet printhead is successfully utilized to direct-write conductive lines with high-viscosity solutions and drop-on-demand print complex pattern with low-viscosity solutions on both insulating and curvilinear substrates. It leads to high-resolution e-jet printing on the arbitrary substrate in a direct, precise and low-voltage manner. The electrostatic lens-integrated printhead thoroughly breaks the restrictions of printing on insulating and nonplanar substrates and significantly broadens its applications.