Tension ring-functionalized bicyclic ammonium ionic liquids as hypergolic fuels with superior energy density.

Cage molecule combined with tension ring to design new ionic liquid molecules. The resulting ionic liquid has higher energy density due to the high angular and torsional tensions of the tension ring. This provides a new way to improve the energy density of rocket bipropellants. [Display omitted] • We propose to combine cage structures with tension rings to design new ionic liquid molecules. • The obtained ionic liquids possess higher energy density up to 1.87 kJ·ml−1. • Ignition delay time of hypergolic ionic liquid containing tension ring has 52.5 % shorter than that of straight-chain alkane. Hypergolic ionic liquids are a new type of liquid propellants, and the energy density is critical to propulsion performance. We propose to combine cage structures with tensile rings to design and synthesize new ionic liquid molecules. Cycloalkane-substituted 1-aza-bicyclo[2.2.2]octane and 1,4-diazabicyclo[2.2.2]octane-like ionic liquids were synthesized using dicyanamide root as an anion, and their structure and properties were determined. The obtained ionic liquids possess higher energy density up to 1.87 kJ·mL−1. The three-membered ring substituent can increase the energy density of ionic liquids by 79.8 % and reduce the ignition delay time by 52.5 % than that of straight-chain alkanes. This work provides an important basis for the design and synthesis of the new type of hypergolic ionic liquids. [ABSTRACT FROM AUTHOR]