Oriented Attachment Growth of 2,6-Diamino-3,5-dinitropyrazine-1-oxide Mesocrystals: Morphological Evolution, Regulation, and Mechanism

The oriented attachment (OA) growth is versatile for structuring materials with desired physiochemical properties, but the mesoscale details of how primary building blocks evolve into a higher-level superstructure remain largely unresolved. Here, we discover a distinct OA growth pathway of a low-sensitivity, high-energetic material, i.e., 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105), by a controlled polymer-assisted crystallization approach. The evolution of the crystal morphology with time shows that LLM-105 mesocrystals composed of mutually oriented nanocrystals form first via OA growth and subsequent transform into single crystals via crystallographic fusion. The length-to-diameter (L/D) ratio of LLM-105 mesocrystals could be tuned by varying the polymer additive (poly(vinyl alcohol), PVA) concentration, such that plate-like morphology with improved coherence strength can be obtained. Both process analysis technology and molecular dynamics simulations indicate that the OA mainly occurs on the (020), (110), and (1–10) faces of primary LLM-105 nanocrystals, where PVA chains are less present. The hydrogen bonding interactions (N–HLLM-105···O–HPVA and/or N–OLLM-105···H–OPVA) are considered the main driving force for the selective chain attachment on the (10–1) face of LLM-105 nanocrystals. This new mechanistic understanding of LLM-105 crystallization provides extra potential for the morphology-dependent property control of energetic crystals.