Passively Focused Electrospray Printing of Polymeric Films

In electrospray printing, strong electric fields are used to atomize a liquid solution into a plume of charged microdroplets containing the print material. Owing to their small size, the solvent rapidly evaporates to leave behind dry particles that are delivered to a target substrate to create a film. Here, we report on the use of a high-throughput electrospray printing system to deploy polyimide onto silicon. Passive electrostatic focusing was used to increase the rate of film growth, resulting in dense particulate films in relatively short print times. The film growth was asymptotic and dependent on the emitter-substrate separation distance. Films printed at a closer separation distance grew more rapidly and had a greater (maximum) thickness than those printed from further away. The functional performance of the films was characterized by wettability and dielectric breakdown testing. The wettability was independent of the print conditions due to the negligible variation in surface roughness, resulting in an average contact angle of 110°. Breakdown potentials exceeding 1 kV were achieved with the thickest films, however the breakdown field strength decreased with increasing film thickness. As such, the thinner films achieved the highest breakdown field strength of ~142 V/??m.