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 [δ(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.
Crystal clogging continues to be a general problem in the tubular continuous crystallization process. We investigated the crystal adhesion mechanism in milliliter-scale tubular crystallizers using experimental and molecular dynamics (MD) methods with glycine as a model compound. The factors that affect crystal adhesion on the surfaces of tubing materials were discussed in terms of chemical and physical properties. The primary factor determining the adhesion and clogging extent in a flowing tubular crystallizer is the interaction energy on the interface of the crystal tubing. Another factor is the roughness of the tubing surface. In addition, the clogging tendency of the two kinds of materials (steel and glass) that are normally used in the industry was predicted and confirmed by employing identical MD and experimental methods. Generally, the clogging tendency of the tubing materials is as follows: steel > silicone rubber > polyvinylidene chloride > polytetrafluoroethylene > glass. This work provides a method for the choice of crystallizer inner surface materials, which will help to solve the clogging problem in tubular continuous crystallizers.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.