Behavior of liquid meniscus in electrospray dependent on voltage waveform

This paper describes the influence of rise-time of the driving voltage on Taylor-cone formation in drop-on-demand electrospray. A thin tapered glass capillary coated by titanium was used as an ejection nozzle where a step-functioned voltage with a various rise-time was applied. The step-functioned voltage was produced by switching on the DC high voltage using a MOSFET module, and its rise-time was adjusted by changing a resistance and capacitance of the discharge circuit. Ethanol was used for the liquid material and slowly delivered to the nozzle tip. Time-resolved microscopic images of the liquid meniscus on the nozzle tip were taken by using the laser shadowgraph method. The Taylor-cone formation time, which is determined by the time difference between the MOSFET turning on and the liquid jet ejection, obviously tends to be reduced by shortening the rise-time of the voltage. This experimental result suggests that shortening the voltage rise-time significantly improves the repetition frequency of drop-on-demand electrospray.