Crystal morphology characterization and initial concentration effect study of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) grown in DMSO solution

Crystal morphology plays a vital role in the properties and performance of energetic materials (EMs). Here, the crystal morphology of 2,6-diamino-3,5-dinitropyrazine-1-oxide (LLM-105) grown in dimethyl sulfoxide (DMSO) solution was characterized using single-crystal X-ray diffraction (SCXRD) and rotation imaging techniques. The exposed facets, especially the terminal ones, were indexed for the rod-like LLM-105 crystal for the first time. The preferential growth direction was determined to be the (100) direction. The morphological importance of the crystal planes is in an order of (011) > (020) > (110) > (101) in a lower initial concentration (0.5 mg/mL) and (011) > (020) > (110) in a higher initial concentration (0.8 mg/mL). The increase of concentration was also found to decrease the growth rate along the (001) direction and increase that along the (010) direction. The terminal facets were investigated in more detail to provide the missing piece to our recent knowledge about the crystal morphology of LLM-105. This experimental observation has also been compared with the crystal morphology of LLM-105 predicted by theoretical simulation. The potential reasons for the discrepancy of the theoretical predictions from experimental observations for LLM-105 have been discussed, and actual concentrations, water effects, and dynamic factors were proposed for the improvement of theoretical simulation. A potential strategy for the morphology control of LLM-105 crystals has been proposed. These results clearly demonstrate the central importance of the experimental characterization data to the rationality verification of the growth model in morphology prediction of energetic crystals before practical application and will benefit the morphology control and performance improvement of LLM-105 and other EMs.