(458f) Designing Composite Energetic Nanomaterials with Tunable Interfacial Activities Via Laser Ablation Synthesis in Solution

Energetic nanomaterials (ENMs) find applications in solid-state propellants and explosives. Yet, the large heat release in the Al nanoparticle (NP)-based first-generation ENMs were offset by hindered detonation rates due to the fuel-oxidizer diffusion lengths and rates being compromised by excessive oxide shell formations and NP aggregations. Efforts have been made tune their energetic behaviors by tailoring their interfacial structures that can control the oxide shell formation while leading to excessive internal stresses within the metallic cores. Yet, there exists weak fundamental understanding and considerable challenges in the rational design and synthesis of such nanostructured architectures. To this end, carbon (C) coatings on Al NPs facilitate safe handing while promoting enhanced activities due to the added advantages of the coating itself oxidizing into gaseous products (CO₂, CO etc.) without any residual ash formation, while allowing the C shell to retard NP aggregations. But, the challenge remains in the facile yet, chemically clean synthesis of these encapsulated NPs without contaminating and/or oxidizing the metal cores. Here, we address this challenge through rational design and structure-property characterizations of graphitic shell coated Al NPs (< 20 nm sizes) dispersed in pyrolyzed C matrices via laser ablation synthesis in solution (LASiS) to preserve high surface areas and interfacial properties of Al NPs. Such nanostructures allow tailored design of interfacial structures that can either lead to strain energy manifestation or, rate-controlled release of solid propellants under high pressure/temperature to prevent oxide shell-mediated surface passivation. Energetic activities of the C/Al composite NPs were tested via Laser-induced Air Shock from Energetic Materials (LASEM) technique at the US Army Research Laboratory, Aberdeen Proving Ground, MD. We demonstrate that synthesis parameters such as organic solvents, laser flux and ablation times can be tuned to provide superior control on NP sizes/aggregation with the aid of the C shell formations and, in turn, their energetic behavior. The study unveils synthesis-structure-property relations in LASiS-based manufacturing of ENMs capsuled in graphitic shells that are safe to handle and undergo kinetically controlled energy release under desired conditions. Such Al/C-based ENMs can be immediately employed for high energy density munitions in defense applications.