The effects of magnetic surface stress on electrospray of an ionic liquid ferrofluid

摘要

Four solutions of an ionic liquid ferrofluid (ILFF) using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-NTG) as the carrier liquid were emitted from a capillary electrospray source and its beam was measured using a time-of-flight mass spectrometer (TOF-MS) and a downstream stack of Faraday plates. The solutions had 3.04, 5.98, 8.80, and 14.15 wt% iron-oxide nanoparticles making them susceptible to magnetic fields. A Helmholtz coil was used to impose a magnetic stress onto the electrospray source. The addition of nanoparticles to neat IL increased viscosity, and decreased conductivity and surface tension of the fluid. The emission current followed the proportionality ~ √QγK, with a slope that depended upon both the concentration of nanoparticles and the magnetic field. The addition of nanoparticles caused an increase in the total emission current from the source when compared to neat IL running at the same flowrate. Conversely, the addition of a magnetic stress decreased the total emission current from the source compared to the field-free case; the change was larger in solutions with a higher wt% of nanoparticles. The magnetic stress also decreased the minimum stable flowrate that could be achieved, widening the operational envelope beyond that of traditional non-magnetic electrospray.