Dynamic simulation of ion evaporation from a conductive meniscus, fluid-fluid model of plume and meniscus interactions

Ion evaporation from a conductive meniscus has been of significant interest in the theoretical investigation of electro-hydrodynamics and application exploration across various fields. This study focuses on developing a fluid-fluid methodology for the dynamical simulation of a conductive meniscus undergoing ion evaporation and uncovering the interaction between the plume and meniscus using the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate as a case study. In the fluid-fluid model, we propose a simplified fluid plume model to acquire the charge distribution in free space, and validate it against a particle plume model and a full fluid plume model. The meniscus evolution is described by expanding the leaky dielectric model to account for charge conservation in the liquid as well as self-heating and inhomogeneous physical properties. The arbitrary Lagrangian–Eulerian method is used to track the sharp liquid–vacuum interface. Dynamic simulation with the simplified fluid plume model is more than 150 times faster than that with the full fluid plume model. The electrohydrodynamic process of the meniscus evolving to form a droplet is analyzed, with a detailed discussion on the space charge effect caused by evaporated ions. Results indicate that neglecting the space charge effect during conical meniscus formation leads to a singular meniscus tip. Instead, the reverse electric field induced by the space charge suppresses this singularity, assisting the conical meniscus to produce a jet. Additionally, the high-throughput ion evaporation significantly enlarges the diameter of droplet formed on the conical meniscus due to the reverse electric field of space charge.