Search

The emissions of Taylor cones from a wide range of ionic liquids (ILs) have been tested in vacuo in an attempt to identify what physical properties favor the purely ionic regime (PIR). This regime is well known in the case of Taylor cones of liquid metals. For non-metallic???? liquids, it has been previously observed in conventional (capillary tube) electrospray sources at room temperature only for the room temperature molten salt (ionic liquid, IL) EMI-BF4 (EMI = 1-ethyl-3-methylimidazolium). A large number of other ILs and their mixtures have been studied here, most of which (but not all) are unable to reach the PIR at room temperature. Based on these results and additional theoretical considerations, strong support is assembled ??? for the notion that the PIR is favored not only by ionic liquids of high electrical conductivity, but also of high surface tension. This hypothesis is confirmed by tests with three recently synthesized ILs EMI-GaCl4, EMI-C(CN)3, and EMI-N(CN)2, all of which combine exceptional surface tension and electrical conductivity, and all of which reach the PIR at room temperature far more readily than EMI-BF4.

The original project goal was to develop sources of heavy ions for space propulsion based on Taylor cones of heated ionic liquids(ILs). Many commercially available heated ILs have been discovered that reach the purely ionic regime (PIR) of emissions (no drops), offering a new high-efficiency ion source for electrical propulsion. A few commercial ILs have been found to reach PIR even at room temperature. Later efforts were directed at identifying and testing many non-commercial ILs capable of PIR at room temperature, especially those with high surface tension and high electrical conductivity, which are found to offer the most favorable conditions for electrical propulsion. Basic understanding of Taylor cones of ILs is still incomplete. But they have been seen to have similar advantages to well know liquid metal ion sources (LMIS) in terms of narrow ion energy distribution and microAmp current levels . ILs actually outperform liquid metals in many ways, as they run in positive and negative polarity, function at room temperature, offer a much wider range of masses and chemical compositions, are generally less reactive than molten metals, and are expected to form less contaminating plumes., Prepared in collaboration with the Massachusetts Institute of Technology, Kyoto University, US Air Force Academy, Jet Propulsion Laboratory, and the Poytechnical University Madrid.