The In-Flight Breakup of Drops Subjected to Electric and Ionic Fields of DC Corona Discharge

In-Flight ElectroSpraying (IFES) is a novel approach to generate electrically charged micrometer-sized and/or nanometer-sized progeny drops in a controlled manner. This is accomplished in ight, beginning with millimeter-sized parent drops. The breakup of charged drops that is exploited in IFES also occurs (sometimes unwantedly) in conventional electrospraying, electrospinning, and electrospray mass spectrometry. An understanding of what controls the break-up of a parent drop into its progenies is essential in estimating the resultant sizes and charges. The results of experiments on the break-up of electrically charged parent drops into progeny drops are described. The break-up occurs in applied electric (1 kV/cm to 10 kV/cm) and ionic (1013/m3 to 1015/m3) elds that are generated using a DC-corona discharge in a needle-plate con guration. The size, velocity, and charge of mm-sized to nm-sized drops are measured for di erent initial parent drop sizes. To predict the distribution of the ion space charge, the current density is measured at di erent positions on the grounded electrode. The e ects of the applied electric eld strength, the ion concentration and the initial drop surface temperature on the drop break-up are quanti ed. Several models also are summarized, including simulations of the electrohydrodynamics of the corona discharge, drop charging, drop trajectory analysis, and an electro-capillary stability analysis of the drop's charged surface. The experiments clearly demonstrate that the charge and size distribution of the progeny drops can be controlled by subjecting speci c-sized parent drops to di erent electric and ion elds. The resultant charge of rst-generation progeny drops is found to vary as d1.5, where d ranges from ∼ 1 μm to ∼ 100 μm, and is independent of the intensity of the applied electric eld and the parent drop size. Similarities of the observed drop inight spraying modes with those of conventional electrospraying from capillaries are noted. Advisor: Patrick F. Dunn