Electrohydrodynamic charge depletion at EMIM-EtSO4 interfaces: Atomistic mechanisms of emission mode transitions under electric fields

WY He and LP Su and ZP Yao and SQ Cui and TG Fang and SQ Li, PHYSICS OF FLUIDS, 37, 112012 (2025).

DOI: 10.1063/5.0296503

Charge transfer and dissipation at the ionic liquid (IL) Taylor cone- vacuum interface critically govern IL electrospray performance, yet remain poorly understood. This study employs the all-atom molecular dynamics method to investigate time-resolved 1-ethyl-3-methylimidazolium ethyl sulfate electrospray behavior and electric field regulation of interfacial charge dynamics. Key findings reveal that increasing electric field strength accelerates Taylor cone formation, extends jet length, and elevates cluster emission proportions-with dimers and larger clusters exceeding 60% at 1.4 V/nm. The average emission current increases from 11.8 to 51.5 nA with field strength, while the specific impulse peaks at 612.18 s at 1.3 V/nm before declining at 1.4 V/nm due to intensified cluster interactions. Under constant-polarity fields, emission processes undergo three distinct stages: monomer emission (stage 1), cluster emission (stage 2), and termination. Stage 1 exhibits increasing current and 23% higher average specific impulse than stage 2, where elevated large-cluster proportions reduce charge-to-mass ratios. Surface charge density decay rates increase monotonically with field strength, resulting in accelerated charge depletion at higher fields. After positive-field emission, immediately applying a negative electric field (-0.2 V/nm) can induce the emission of large droplets and anion clusters. In the subsequent cycle, positive fields successfully reignite cation emission but with diminished currents. This work establishes the fundamental stepwise IL ion emission mechanisms, providing theoretical foundations for the IL electrospray optimization.

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