Molecular Dynamics Simulations of Ion Extraction from Nanodroplets for Ionic Liquid Electrospray Thrusters

Abstract

Molecular dynamics (MD) simulations were performed for ion extraction from electrospray thrusters to investigate relevant extraction processes numerically. To approximate the electrospray jet tip, a simulation domain consisting of 4-5 nm-sized ionic liquid droplets was used. The extracted ion angles and kinetic energies from EMI–BF4 (1-ethyl-3-methylimidazolium tetrafluoroborate) and EMI–Im (1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide) droplets were quantified by applying uniform electric fields of 1.3–1.7 V nm−1. The MD simulations are in great agreement with simulations presented in the literature and consistently show a greater preference for monomer emission than reported experimentally. At field strengths above 1.5 V nm−1, apparent droplet fracturing and breakup lead to an increase in ion angular velocity distributions. Greater mobility of EMI–BF4 ions than EMI–Im was also observed, indicative of the crucial role of cation-anion hydrogen bond strengths in ion extraction and beam composition between different propellants.

Structural Properties of HEHN- and HAN-Based Ionic Liquid Mixtures: A Polarizable Molecular Dynamics Study

“…Reactive bulk-phase systems may undergo proton hopping (cf. Grothuss mechanisms) that perturb H-bond networks and ion transport. , Moreover, previous MD simulations show that ILs’ response to external electric fields may induce a wider range of possible breakdown mechanisms, from evaporation to fission, that are especially relevant to understanding electrospray thrusters. ,,− Consequently, the geometric conditions and stability of H-bonding from Figure and Table serve as essential prerequisites toward developing accurate reactive force fields which, in turn, inform parameters in many reduced-order thruster performance models. − …”