Vacuum electrospray ionization study of the ionic liquid, [Emim][Im]

Chiu, Yu‐Hui; Gaeta, Geraldine; Levandier, Dale J.; Dressler, Rainer A.; Boatz, Jerry A.

doi:10.1016/j.ijms.2007.02.010

Cited by 73 publications

(89 citation statements)

References 40 publications

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“…Thus, the derived average m/q value is only representative of charge emission captured at small angles with respect to the capillary axis. The nonuniformity reported by Chiu et al for the ionic liquid, [Emim][Im], 51,52 is consistent with predictions that the surface electric field is highest at the cone-jet neck, where field-evaporated ions are driven away from the cone-jet axis. 41,43 The respective field-evaporated ions are, therefore, preferably emitted at large angles whereas droplets, emitted from the jet tip, have narrow angular distributions centered on axis.…”

Section: Discussionsupporting

confidence: 83%

“…This somewhat surprising result can be explained by the substantial decrease in charged particle beam divergence upon dilution, as reflected by the ratio of the Faraday Cup current with respect to the total emitted current. As angular distribution measurements on ionic liquid cone-jets operated in a nano regime have shown, 51,52 the m/q distribution can be nonuniform with respect to the emission polar angle. Thus, the derived average m/q value is only representative of charge emission captured at small angles with respect to the capillary axis.…”

Section: Discussionmentioning

confidence: 99%

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Nanojets, Electrospray, and Ion Field Evaporation: Molecular Dynamics Simulations and Laboratory Experiments

et al. 2008

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The energetics, interfacial properties, instabilities, and fragmentation patterns of electrosprays made from formamide salt solutions are investigated in a mass spectrometric vacuum electrospray experiment and using molecular dynamics (MD) simulations. The electrospray source is operated in a Taylor cone-jet mode, with the nanojet that forms being characterized by high surface-normal electric field strengths in the vicinity of 1 V/nm. Mass-to-charge ratios were determined for both positive and negative currents sprayed from NaI−formamide solutions with solute−solvent mole ratios of 1:8.4 and 1:36.9, and from KI−formamide solutions with mole ratios of 1:41 and 1:83. The molecular dynamics simulations were conducted on isolated 10 nm NaI−formamide droplets at mole ratios of 1:8 and 1:16. The droplet was subjected to a uniform electric field with strengths ranging between 0.5 and 1.5 V/nm. Both the experiments and simulations demonstrate a mixed charge emission regime where field-induced desorption of solvated ions and charged droplets occurs. The macroscopic parameters, such as average mass-to-charge ratio and maximum surface-normal field strengths deduced from the simulations are found to be in good agreement with the experimental work and consistent with electrohydrodynamic theory of cone-jets. The observed mass spectrometric Na+ and I− solvated ion distributions are consistent with a thermal evaporation process, and are correctly reproduced by the simulation after incorporation of the different flight times and unimolecular ion dissociation rates in the analysis. Alignment of formamide dipoles and field-induced reorganization of the positive and negative ionic charges in the interfacial region are both found to contribute to the surface-normal field near the points of charge emission. In the simulations the majority of cluster ions are found to be emitted from the tip of the jet rather than from the neck region next to the Taylor cone. This finding is consistent with the experimental energy distributions of the solvated ions which demonstrate that indeed most ions are emitted closer to the jet region, that is, beyond the cone-neck region where ohmic losses occur. This observation is also consistent with continuum electrohydrodynamic predictions of cluster-ion evaporation at surface regions of high curvature and therefore maximum surface electric field strengths, which may be the cone-neck region, the breakup region of the jet (usually near the tip of the jet), or the emitted charged droplets. In the nanoscale jets observed in this study, the regions of highest spatial curvature are at the ends of the jets where nascent drops either are forming or have just detached. The energetics, interfacial properties, instabilities, and fragmentation patterns of electrosprays made from formamide salt solutions are investigated in a mass spectrometric vacuum electrospray experiment and using molecular dynamics (MD) simulations. The electrospray source is operated in a Taylor cone-jet mode, with the nanojet that form...

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Section: Discussionsupporting

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Nanojets, Electrospray, and Ion Field Evaporation: Molecular Dynamics Simulations and Laboratory Experiments

et al. 2008

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“…Preliminary attempts to measure thrust in a unipolar (no alternation) configuration were unreliable as the emission current tended decayed dramatically, by over 40 % at times, and did not tend to fully recover even after subsequent operation with alternation (in contrast to Ref. [37]). Hence, a potential alternation scheme has been adopted.…”

Section: Potential Alternation Schemementioning

confidence: 99%

“…Energy deficits may include intrinsic physical mechanisms, such as the ion solvation energy and Ohmic losses at the Taylor cone apex, or external influences such as series resistances upstream electrical path. Some such losses may not be constant over species mass [37]. In this study the impact of such variability was small and average fractional energy deficits were assumed for the entire spectrum.…”

Section: Indirect Performance Calculationsmentioning

confidence: 99%

“…These liquids were selected due to existing heritage with ILISs in the literature (for example see [34,37] and [7] for studies of EMI-Im and EMI-BF 4 respectively). Furthermore the heavier negative ion mass of Im − (280.2 Da) versus BF − 4 (86.8 Da) and possibility of droplet (or at least very large n) emissions [37] were expected to yield higher thrusts at the expense of polydispersive efficiency. The two EMI-Im and single EMI-BF 4 sources are hereafter referred to as SRC-Im-1, SRC-Im-2 and SRC-BF 4 respectively.…”

Section: Source Preparationmentioning

confidence: 99%

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Comparing Direct and Indirect Thrust Measurements from Passively Fed Ionic Electrospray Thrusters

Courtney

Dandavino

Shea

2016

Journal of Propulsion and Power

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Highly ionic beams of several hundred μA per cm 2 have been measured from porous glass ionic liquid electrospray sources fabricated using a conventional mill. The thrust output from three prototype devices, two emitting the ionic liquid EMI-Im and one emitting EMI-BF 4, was measured directly using a precise balance. Thrusts up to 50 μN were measured when emitting EMI-Im in a bipolar, alternating potential configuration at less than 0.8 W input power and with propellant supplied from an internal reservoir. Measurements of mass spectra via Time of Flight spectrometry, angle resolved current distributions, ion fragmentation and energy deficits have been applied to accurately calculate thrust and mass flow rates indirectly from the same devices. For two of three cases, calculated and directly measured thrusts were in agreement to within a few μN at input powers from 0.1 W to 0.8 W . Emissions of EMI-BF4 are shown to yield nearly purely ionic beams supporting high propulsive efficiencies and specific impulses, ∼ 65 % and > 3200 s respectively at 0.5 W . Conversely, greater polydispersity was observed in EMI-Im emissions, contributing to reduced specific performance, ∼ 50 % propulsive efficiency and ∼ 1500 s specific impulse at 0.5 W .

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Molecular Simulation of Ionic Liquids: Where We Are and the Path Forward

Shah

Maginn

2014

Ionic Liquids Further UnCOILed

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Vacuum electrospray ionization study of the ionic liquid, [Emim][Im]

Cited by 73 publications

References 40 publications

Nanojets, Electrospray, and Ion Field Evaporation: Molecular Dynamics Simulations and Laboratory Experiments

Nanojets, Electrospray, and Ion Field Evaporation: Molecular Dynamics Simulations and Laboratory Experiments

Comparing Direct and Indirect Thrust Measurements from Passively Fed Ionic Electrospray Thrusters

Molecular Simulation of Ionic Liquids: Where We Are and the Path Forward

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