Modern Approaches to the Development of Energetic Materials

Abstract

Energetic materials (EMs) are compounds and compositions that respond rapidly to stimuli by releasing large amounts of gases and energy. These materials are typically central to a variety of commercial and military applications. However, some traditional and widely used energetic materials have toxic decomposition products and can be dangerous to handle due to impact sensitivity issues. One of the major goals for the energetics field is to develop more eco-friendly (non-polluting or readily degradable in the environment) materials that exhibit performance comparable to widely used energetic materials. An emerging class of energetics based on high-nitrogen materials promise to avoid the issues of traditional EMs. Some of the key properties of energetic materials include: oxygen balance, decomposition temperature, detonation velocity and detonation pressure. The stringent requirements for cost, manufacturability and performance are constraints such that new chemical entities are rarely introduced to the market. Here, crystal engineering strategies are employed to design new materials with desired physical and chemical properties. Crystal engineering is unique in being able to leverage existing manufacturing infrastructure for energetic materials. However, one must first uncover the fundamental rules of how energetic molecules interact to develop a design strategy. The work presented in this dissertation focuses on the advancement of modern strategies used to develop new energetic materials through supramolecular synthesis. Through the design of new energetic compounds and compositions, this investigation aims to improve undesired properties of existing energetic materials like toxic decomposition products and oxygen deficiency. Chapter 2 covers work that examines methods of cocrystal engineering with a high-nitrogen energetic material known as BTATz. Cocrystals are not known for many energetic materials and within the class of high-nitrogen molecules the quantity is even more limited. This is because the types of coformers suitable for cocrystallization with high-nitrogen energetics have not yet been elucidated. In this chapter, it is shown that high-nitrogen energetics can in fact form cocrystals and classes of molecules capable of interrupting strong intermolecular interactions are identified. In addition, theoretical energetic performance calculations are discussed. Synthesis of energetic coordination polymers represents a straightforward development approach wherein energetic ligands are coordinated to non-toxic metal ions to produce new metal-organic species. In Chapter 3, an effort towards generating multi-dimensional energetic coordination polymers with the high-nitrogen ligand, BTATz, is detailed. This approach is discussed as an effective means to synthesize energetic coordination polymers that directly incorporate high-nitrogen energetic materials as ligands. The pores of non-energetic metal-organic frameworks can be accessed for the adsorption of over oxidized guests to yield energetic compositions with adjustable oxygen content and modulated properties. In Chapter 4, the development MOF-oxidant composites utilizing zeolitic imidazolate frameworks (ZIFs) as porous hosts are presented. ZIFs are robust and thermally stable structures and two frameworks, ZIF-8 and ZIF-70 were used to absorb volatile tetranitromethane guests. The resultant ZIF-TNM composites exhibit high-energy release and more neutral oxygen balances relative to the porous frameworks. Finally, Chapter 5 will offer a summary on future directions that could be pursued in the development of new high-nitrogen energetic materials.