The influence of mixed solvents on the morphology of ε-CL-20 crystal

CL-20 (especially the ε-crystal form) is a high-energy density explosive, but the preparation of centimeter-sized ε-CL-20 crystals is complex, which limits the study of its properties and mechanisms. Since crystal morphology can significantly affect the performance and sensitivity of energetic materials, this study combines MD simulation and experimental techniques to study and examine the differences in ε-CL-20 crystal habit as well as the interplay between the principal growing crystal planes of ε-CL-20 and the mixed solvent molecules. The findings reveal that according to the AE model, ε-CL-20 consists of (0 1 1), (1 1 0), (1 0 -1), (1 1 -1), (0 0 2), (0 2 1), and (1 0 1) seven independent surfaces under vacuum, and the (0 1 1) surface is the most important growth surface. During the crystallization process of ε-CL-20 in three mixed solvents, the (0 1 1) surface remains an important crystal surface due to its low modified attachment energy. Also, the impact of the solvent component on the morphology of the crystal is more significant compared to that of the non-solvent component. The size of the crystal cultured in the experiment can reach centimeter level and is consistent with the simulated morphology. The X-ray diffraction patterns show that the synthesized crystals were in the ε form, and the sections are (0 1 1) surface. This study provides a novel approach for cultivating large ε-CL-20 crystals, paving the way for further studies on its performance and mechanism.

The ε-CL-20 crystal morphologies were obtained within a vacuum and different binary mixed solvent environments under COMPASS force field utilizing the AE model via the MD method on the Materials Studio 2019 platform. The complete simulation was generated using the NTV system. The temperature control method was chosen as Anderson, whereas the temperature of the system was set as 298 K. The data were acquired after every 5000 steps and the step size was 1 fs, while the total time of the simulation was equal to 100 ps.