Molecular dynamics studies of ionic liquid-surface interactions for electrospray thrusters

Abstract

Electrospray thrusters are of particular interest for micropropulsion because of their compactness, high specific impulse, and their ability to operate over very long periods of time. However, particles on the periphery of the plume are susceptible to collide with the extractor grid, which may reduce the efficiency and limit the lifetime of the electrospray thruster. Therefore, a thorough characterization of the collision process and byproducts is crucial to understanding the long-term surface effects and overcoming the lifetime-limiting mechanisms. This study attempts to investigate particle impingement on the extractor grid using molecular dynamics simulations with two different models. The first model is based on a non-reactive force field and is used to investigate the dissociation of ionic bonds. The second model is based on a reactive force field and is used to investigate the breaking of covalent bonds. In both cases, a statistical analysis is carried out over the initial configuration of the molecule. The major results of this study are: (1) the inference of probability curves of the ionic dissociation in function of the impact energy for temperatures ranging from 300K to 1000K, and (2) the prediction of mass spectra of the byproducts post-collision. The probability curves indicate a strong correlation between the impact energy and the ionic dissociation for energies smaller than 60 eV. The predicted mass spectra indicate that strong collisions are more likely to produce light byproducts whereas weak collisions tend to produce heavier molecules.