Perfect Energetic Crystals with Improved Performances Obtained by Thermally Metastable Interfacial Self-Assembly of Corresponding Nanocrystals

The interfacial self-assembly of energetic nanocrystals was proposed and systematically studied in this work. Effects of the reaction temperature, grain size of nanocrystals, solvent system, and addition of surfactant on the self-assembled crystals were investigated. The morphologies and crystal structures of the self-assembled products were investigated by microscopy analysis and coherence strength tests. Furthermore, the energetic crystals prepared by a thermally metastable self-assembly method were systematically compared with the starting raw crystalline materials and the corresponding crystals prepared by recrystallization, in terms of polymorphic transition behaviors, impact sensitivity, and thermal properties. It has been shown that the energetic crystals synthesized by this novel self-assembly method were uniform with smooth surface and free of defects. These crystals also had very narrow size distribution, ordered crystallographic texture, and high compactness, with significant improvement in impact sensitivity. It is suggested that the polymorphic transition of energetic crystals can be favorable, but it is not essential to reach the thermally metastable state before nanocrystal assembly, resulting in higher thermal stability. The kinetics of the self-assembly process were found to follow the Avrami equation. The possible mechanism of this self-assembly process was also proposed, including, sequentially, solvent induction originated from surface solvation or localized dissolution, particle aggregation, and interfacial crystal growth.