Electrospray Printing of Polymeric Films onto Substrates with Non-Homogenous Electrical Properties

Electrospray printing is an additive manufacturing technique for creating thin polymeric films. A unique aspect of electrospray is that the electrical properties of the target substrate govern the thickness of the film. For example, a thicker film will be created on conductive portions of a surface compared to sections that are insulating. In this work, polyimide is delivered to a glass substrate with a periodic array of patterned gold electrodes. The emitted particles track the electric field lines from the electrospray nozzle to the grounded electrode array. The polymer is preferentially deposited onto the gold surface and is defined by a preference ratio (i.e. gold versus glass deposition). A comparison is made with an ungrounded electrode array, which showed thinner films but still a very high preference ratio. By tuning the flow rate of the precursor solution, a range of film thicknesses and microstructures are obtained. For sufficiently high flow rates, the precursor solvent does not fully evaporate in-flight, resulting in the polymer depositing in a semi-dry state. This modified the microstructure of the films, creating a thinner layer with higher density. The function of the printed films is characterized by measuring their adhesion and dielectric breakdown strength.