High Frequency AC Electrospraying of Dielectric Liquids

A new high-frequency (> 10 kHz) AC electrospray phenomenon which behaves distinctly to DC electrosprays is investigated. Unlike DC electrosprays, the drops do not emanate from the usual well-defined Taylor cone-jet and carry no net charge. Instead, the meniscus vibrates at a resonant frequency associated with its capillary-inertia vibration time, periodically ejecting drops with dimensions of order 10 μm under the action of the Maxwell-Wagner electric stress at the meniscus tip. Above a crossover frequency, the polarization and direction of the Maxwell force reverses and an apparent electrowetting effect is observed. A simple lubrication model is used to generate spatio-temporal evolution profiles for the stretched liquid meniscus tip as a function of the Maxwell-Wagner stress and a capillary number. From a self-similar scaling technique, the meniscus is shown to advance as t^1/2.