Molecular Dynamics Study on Temperature-Dependent Ion Transport in Wetted Ionic Liquid Thrusters

Ionic liquid electrospray thrusters (ILETs) face significant challenges in extreme space environments because the thermophysical and transport properties of ionic liquids (ILs) are temperature sensitive and can directly affect electrospray behavior. In this work, molecular dynamics (MD) simulations were employed to elucidate the temperature-dependent ion transport, initial emission dynamics, and near-tip plume characteristics of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) on externally wetted silicon emitters. The results demonstrate that elevated temperature enhances ion mobility while reducing surface tension, indicating coupled effects on ion replenishment and meniscus stability. A synergistic regulation of field-driven ion transport by temperature and electric-field polarity was observed: positive fields preferentially promote cation transport, whereas negative fields enhance anion mobility at low temperature. Increasing temperature shortens the initial emission response time and increases the MD-domain apparent specific impulse and emission current, but concurrently exacerbates plume divergence and induces ion cluster formation, which can reduce the apparent specific impulse. Within the present nanoscale MD model and the specific metrics considered here, maintaining BMIM-PF6 within 295-335 K provides a favorable balance among ion supply, response time, apparent propulsion performance, and plume divergence; this range should be interpreted as model-specific guidance rather than a universal optimum for complete ILET devices.