Hypergolicity evaluation and prediction of ionic liquids based on hypergolic reactive groups

Abstract

Three hypergolic ionic liquids, anion dicyanamide ([DCA]), cyanoborohydride ([CBH]) and thiocyanate ([SCN]) combining with cation 1-allyl-3-methyl imidazolium ([AMIM]), are prepared to explore the hypergolicity of ionic liquids in our work. Their viscosity, density, melting point, energy properties and specific impulse are measured and calculated. Ignition delay time (IDT) and combustion phenomenon are obtained with a high speed camera to show the hypergolicity. Their energy gaps (∆E), initial ignition reaction free energies (∆rG) and enthalpies (∆rH) are calculated at Gaussian 09 and compared with those of other seven reported hypergolic ionic liquids. The results show hypergolic anions usually possess smaller ∆E than non-hypergolic anions. And IDT and ∆E of three synthesized hypergolic anions have the same order: [CBH] < [DCA] < [SCN]. The hypergolic reactive groups (HRGs), such as B-H, are first proposed as the source of hypergolicity. The numbers and types of these groups will influence the hypergolicity and greatly determine the ignition delay time of ionic liquids. A hypergolicity evaluation scheme is established in this paper to predict the hypergolicity and guide the design of new hypergolic ionic liquids.