Stabilization of monodisperse electrosprays in the multi-jet mode via electric field enhancement

The electrospray of conducting liquids operated in the cone-jet mode is well known to have the unique ability of generating droplets uniform in size over a phenomenal range of sizes depending primarily on the liquid flow rate and physical properties. Since there is a monotonic dependence of size on flow rate, the liquid flow rates that can be dispersed are modest if the goal is to produce very small (below a few micrometers in diameter) droplets. Yet, this is precisely the application niche for which few, if any, atomization alternatives are available. Multiplexing the spray source is indispensable for the electrospray capabilities to have an impact in high-value-added applications. We report here on a novel approach to multiplexing based on a well-known, but hitherto unexploited, regime of operation, the multi-jet mode. Ordinarily, such a mode is rather unsteady and the range of flow rates at which appreciable multiplexing is achieved is small. However, if the multi-jet mode is anchored by some sharp features (e.g., grooves, ridges, etc.) machined at the outlet of the atomizer, to intensify the electric field at discrete points around its perimeter, then the cone-jets are simultaneously anchored at these features and a stable mode of operation is identified over several hundreds of volts and a broad range of flow rates. Most importantly, so long as the machining is accurately reproduced from point to point, droplets generated do not vary significantly in size from spray to spray. As a result, a compact, inexpensive and versatile multiplexing system is realized without sacrificing droplet monodispersity. (C) 2005 Elsevier Ltd. All rights reserved.