<i>Ab initio</i> simulations of dynamics of EMI-BF4 ionic liquid propellant used in electrospray thrusters for nanosatellite applications

Detailed quantum-chemistry calculations of field-induced fragmentation reactions of ionic liquids are presented. The simulations identified the most likely channels for hard (breaking covalent bonds) fragmentation. The computed energetics for hard and soft (breaking clusters into moieties) fragmentation can be incorporated in multiscale models of thrusters' operation. The simulations determined that soft fragmentation occurs on a picosecond timescale, revealing that these large and flexible ions can be heated when accelerated by the electric field. Although the acquired internal kinetic energy is not sufficient to break covalent bonds in cold molecules, it can result in the fragmentation of hotter molecules. The results contribute to a better understanding of processes occurring in thrusters that use ionic liquids as propellants and suggest that deviations from the idealized behavior of the propellant (as charged point-mass particles) in the acceleration region might be important. The results of this study provide a foundation for further improvement of multi-scale models of thrusters' operation.