Discharge in electrospraying of highly conductive aqueous solution coated with outer ionic liquid

Discharge in electrospraying can be applied in water decontamination, dental sterilization, and spectrometry of biological samples. The discharge in electrospraying of a single liquid like the aqueous solution or the ionic liquid has been investigated, which presents different discharge characteristics such as patterns, currents and frequencies. This paper puts forward a way to actively control the discharge characteristics of liquids electrospray beyond the limitation of their own physical properties, which was accomplished by utilizing the technique of coaxial electrospray to coat the concentrated sodium chloride (NaCl) aqueous solution with a layer of ionic liquid. Previously we used this method to suppress the discharge of NaCl solution and stably electrosprayed the NaCl solution. The discharge characteristics of coaxial electrospray and the effect of the applied voltage and the flow rates of both liquids on the discharge was investigated in detail. When being electrosprayed, the NaCl solution alone discharged with pre-onset mode, pulseless corona discharge mode and streamer discharge mode, while the ionic liquid and the coaxial electrospray only discharged with the streamer discharge mode with a conical liquid shape, and less droplets were formed during the transient cone-jet emission. After being coated with the outer ionic liquid, the current, frequency and onset voltage of the discharge of the inner aqueous solution all increased. The current and frequency of the discharge of the coaxial electrospray all increased as the applied voltage increased. In addition, a numerical simulation has been conducted, which confirmed that the inner aqueous solution was strongly shielded from the external electric field by the outer ionic liquid layer. Therefore, it is plausible to actively control the discharge characteristics of the liquids through adjusting the flow rates of both liquids, the applied voltage and choosing the suitable outer liquid.