Uncovering the Morphological Regulation Mechanism of Low Sensitivity and Highly Energetic Materials in Solvents: Changing Crystal Morphology Induced by Hydrogen Bonding

Low sensitivity and highly energetic materials (LSHEMs) are currently the most promising high-energy materials due to their structural stability. However, many problems exist due to their abundant hydrogen bonding (HB) in the structure, such as low solubility and difficulty controlling the crystallization process. In this paper, aiming at regulating the crystal morphology of LSHEMs, 4,4',5,5'-tetranitro-1H,1'H-[2,2'-biimidazole]-1,1'-diamine is used as a model substance to explore the mechanism of controlling the crystal morphology in solvents. The molecular structure, crystal structure, and HB sites on crystal faces were investigated by molecular electrostatic potential surface, Hirshfeld surface, and HB analyses, and it was found that the HB density [delta(HB)] of faces is of the order (011) > (11-1) > (110) > (100) in crystal or solution, determining the tendency of interaction with polar solvents. Then, using molecular dynamics simulation and the modified attachment energy model, we found that the attachment energy of crystal faces and the predicted crystal morphologies in different solvents were determined by HB sites on faces and strongly correlated with the solvent polarity. The experimental morphologies were consistent with the trend predicted including the aspect ratio trend, which confirmed our theoretical speculation. This work provides an effective method of choosing solvents for morphology customization of LSHEMs, which will help guide the morphology control and realize the industry application of LSHEMs.