Meniscus dynamics and jetting transitions in pulsatile flow electrosprays

Jetting in electrosprays results from the interplay of surface tension and electrostatic forces acting on a liquid meniscus. Rayleigh-type capillary waves govern interfacial dynamics of classical pulsating electrosprays and synchronize jetting with meniscus extrusion. We have been using a resonant mechanical actuation of the electrospray emitter to generate periodic pressure waves and produce controllable meniscus deformation, while a superimposed electric field assists in driving singularity formation. It is suggested that the mechanical actuation across various pulsatile flow fields [governed by the Womersley number, WO=R*(ωρ/μ)1/2, where ω is the angular frequency of flow fields, ρ and μare the density and viscosity of the liquid, and R is the nozzle radius] would modulate interfacial behavior under combined hydrodynamic and electrostatic effects. To explore meniscus response across distinct inertial–viscous regimes, a piezoelectric actuator was used to generate pulsatile flow at three representative Womersley numbers. Jetting frequencies, liquid volume deposition, and liquid jet morphologies were studied across small, intermediate, and large Womersley numbers. The electric field remained below the jetting threshold in the absence of flow. High-speed imaging captured interface deformation, and numerical simulations resolved the corresponding pressure and velocity fields.Unlike classical systems, the pulsatile flow electrospray exhibits distinct meniscus dynamics that vary across the range of Womersley numbers. While jetting is always synchronized with the extrusion of the pulsating electrospray meniscus, we observed jetting during meniscus withdrawal at intermediate Womersley numbers. A phase diagram captures transitions to and from low and high Womersley numbers, where ejection remains synchronized with the meniscus extrusion. Simulations and imaging corroborated that pulsatile flow governs interface dynamics, while the electric field sharpens the meniscus and facilitates the development of the singularity.