Electrospray Printing of Polyimide Films Using Passive Material Focusing

In electrospray printing, a high electric potential is used to atomize a liquid solution containing the print material into a spray of charged microdroplets. Rapid solvent evaporation from the droplets renders a spray of charged dry particles that are directed onto a target substrate to print a film. Here, we report on electrospray printing of polyimide, an important polymer in electronics manufacturing, aerospace, and environmental applications. Using a passive electrostatic funnel to focus the print material, films were printed with thicknesses of more than 15 mu m. However, the use of the funnel resulted in a significant amount of material deflected away from the target. The separation distance from the emitter to the target substrate was a key print parameter, resulting in different rates of film growth at different distances. The film growth was asymptotic, leading to self-limiting thickness due to the accumulation of electric charge in the film. The functionality of the printed films was evaluated by measuring their wettability and dielectric strength. The films maintained consistent surface wettability for a range of print conditions and film thicknesses. Weibull reliability analysis was performed for characterizing the dielectric strength of the printed films. The thickest films could sustain the highest applied potentials, exceeding 1 kV; however, the probability of breakdown increased with increasing electric field strength. As a result, thinner films had a greater breakdown electric field strength of similar to 142 V/mu m.

Automated summary

In electrospray printing, a high electric potential is used to atomize liquid solution and print onto a target substrate. The use of a passive electrostatic funnel helps focus the print material, though it also results in material deflection from the target; furthermore, the distance from the emitter to the target substrate is a key print parameter affecting film growth rates.