Utilizing 2D metal halide perovskite thin films as highly tuneable surfaces for orientation control of energetic materials†

The development of high performing and stable energetic materials (EMs) is a focus for a variety of applications including explosives, propellants, and pyrotechnics. To enhance stability, energetic crystals are often interfaced with materials such as chemical binders, which can introduce a variety of physiochemical phenomena ultimately leading to unpredictable stability and performance within the composite. Therefore, a thorough understanding of how energetic crystals behave when interfaced with various chemical functionalities is crucial for designing safer, high performing energetic formulations. This work provides a fundamental insight into interactions between a high performing energetic material, CL-20 (hexanitrohexaazaisowurtzitane), and other materials' surfaces. Highly controlled, tunable 2D metal-halide perovskite (2D MHP) templates with tunable periodicity and chemistry were created and used as a template layer to influence nucleation and growth of CL-20 crystals. All MHP/CL-20 bilayer films exhibit small, nonuniform crystalline deposit morphology for the CL-20 crystals with β-CL-20 polymorphic structure. While most MHP films template the formation of β-CL-20 crystals with a (111) preferential orientation, PbPMA₂Cl₄/β-CL-20 films crystallize with a (020) preferential orientation. The results presented herein suggest interfacial energy minimization between the two bilayer components is the dominant driving force behind the CL-20 preferential orientations. This methodology can potentially be used for developing techniques for growing energetic crystals with desired morphology, packing density and crystallographic orientation.