On the physical mechanisms of multi-jet initiation and mode transition in linear slit emitter

Point emitters have long been the most common electrospray geometry, but their discrete emission sites limit scalability and complicated inter-jet interactions. Annular slit emitters overcame this limitation by distributing multiple jets around a closed perimeter, but optical access remained challenging. A linear slit emitter retains the advantages of a continuous liquid edge while allowing full visualization of the entire emission line. High-speed imaging reveals that jet initiation proceeds through periodic perturbations that sharpen into Taylor cones, with emission modes governed by field distribution and inter-jet interactions. Two reproducible regimes are identified, an outer and an inner cone-jet mode, each with distinct onset thresholds and geometric signatures. The outer cone-jets were observed over a broader operating window, spanning voltages of 16–21 kV and flow rates of 8–20 ml/h, while the inner cone-jets required more stringent conditions of 18–22 kV and 8–18 ml/h. Building on our annular emitter studies, the linear slit geometry uniquely enables direct observation of charge redistribution, pattern formation, and hysteretic mode switching. The findings explain the mechanism of instability-driven and time-dependent multi-jet formation as well as lay the groundwork for scalable electrospray arrays and controllable thrust generation at greater values.