Understanding the effects of molecular additions in energetic ionic liquids
Ionic liquids (ILs) have been utilized in a multitude of areas breaking past the traditional thoughts of ILs only useful as conventional solvents. Recently researchers have been constantly attempting to push and break past the current boundaries of how we think about and exploit ILs as energetic materials. Ionic liquids provide a modular platform that can be changed at the molecular level to take advantage of targeted physical and chemical properties to form energetic materials suitable for use by the Air Force Office of Scientific Research (AFOSR). This work sought to utilize this modular platform to target physical and energetic deficiencies in the ILs through subjecting the ILs to the addition of molecular aromatics. The driving force for the aromatic selection also allowed for tunability of energetic properties within the IL-aromatic mixture. First, an investigation of the interactions among aromatics and ionic liquids, leading to the formation of liquid clathrates, for the targeted modification of the IL platform's physical and chemical properties. ILs' liquid clathrate forming ability is utilized to target the ILs' inherent deficient physical properties in regards to being considered as an energetic material. In this work, the ILs' high viscosity was targeted while maintaining the other inherent attractive properties of the IL (density, melting point, and hypergolicity). Liquid clathrate formation is a powerful tool in viscosity reduction as the IL-aromatic intermolecular interactions help to reduce the ion-ion intramolecular interactions in the IL. The aromatics being used to form the liquid clathrates also traditionally have good space filling abilities in a crystal lattice lending to the density of the liquid clathrate being very close to the original parent IL. Secondly, the molecular level interactions between the ions and the aromatic in the complexed liquid clathrate form can be utilized to tailor the hypergolic reactivity of the material. Theoretical calculations and modeling are used in conjunction with a plethora of experimental spectroscopy and hypergolicity measurements to shed some light on the crucial properties for hypergolic ignition. This work shows the donation of electron density from the dicyanamide ([DCA]^-) anion, which is what initiates the hypergolic decomposition pathway with white fuming nitric acid (WFNA), to the aromatic imidazolium cation in the presence of an aromatic in the complexed liquid clathrate form and provides a theoretical and experimental platform to modify these liquid clathrates for future energetic materials.