Pressure dependence of drop size in electrohydrodynamic inkjet printing

We present the pressure dependence of drop size in electrohydrodynamic(EHD) inkjet printing. A commercial dye ink in an ink reservoir was printed on an aluminum-coated silicon wafer by applying an electrostatic field between a Pt wire inserted in a capillary and the substrate. The Pt wire was connected to an high voltage amplifier and a DC high voltage up to 2 kV was applied to the wire, while the substrate was connected to the electrical ground. The distance between the capillary and the substrate was 2 mm. We observed a micro-dripping mode with a jetting frequency of 1.5 kHz by high speed camera, which doesn't change with the pressure or bias voltage. The size of the drop printed on the substrate increases with the pressure in the reservoir and the bias voltage changes the shape of jetting.