Electrospray emission from nonwetting flat dielectric surfaces

Electrosprays are devices in which nanometer sized droplets and/or solvated ions are electrically extracted from a liquid surface and accelerated to high velocities. They are usually constructed from conductive capillaries with one of the ends tapered down to a sharp tip with the purpose of enhancing the local electric field that produces the instability that develops into the Taylor cone structure from which emission occurs. In an alternative configuration, the conductive needles are replaced by small holes through a dielectric, nonwetting flat block. An electrostatic model shows that if the emitter material has low dielectric constant then the local electric field near the emission site is enhanced in a very similar way as with sharp metallic needles. Furthermore, the combination of the nonwetting property of the material and the sharp corner formed in the hole–surface interface effectively anchors the Taylor cone to the edge of the hole, thus simplifying the process of manufacturing. The possible microfabrication of this configuration makes it especially attractive for producing arrays of large numbers of individual emitters. Such arrays may find use as space propulsion thrusters and in the analytical industry to improve the characteristics of mass-spectrometric analyses.