Crystal morphology control and performance characterization of FOX-7 using natural deep eutectic solvents

Two NADES were used as green recrystallization media for FOX-7 morphology control. • Solute loading is a major factor in reducing aspect ratio. • DES2 shows more weak interaction sites and stronger adsorption with FOX-7. • The mechanical sensitivity of the recrystallized samples is reduced. To overcome the safety and environmental limitations of conventional recrystallization solvents, two natural deep eutectic solvents (DES1 and DES2) were employed for the green recrystallization of 1,1-diamino-2,2-dinitroethylene (FOX-7) to tune its crystal morphology. Key parameters, including the initial solution concentration, antisolvent volume, cooling rate, and stirring rate, were optimized via orthogonal experimental design. IGMH and interaction energy analyses revealed that DES2 had more weak interaction sites with FOX-7 (four vs. three) and stronger interactions than DES1, thereby inducing the formation of a highly rough surface morphology. The resulting products, S-DES1 and S-DES2, both retained the pristine crystal phase. In terms of mechanical sensitivity, the friction load increased from 228 N to 300 N and 336 N for S-DES1 and S-DES2, respectively, while the impact energy increased from 13 J to 34 J only for S-DES2, with no significant change for S-DES1. The compressive resistance (compaction stress of the pressed pellets) reached 5.2 MPa and 5.6 MPa, respectively. The 5 s delay explosion temperature increased from 581 K to 586 K and 597 K, indicating a marked decrease in thermal sensitivity. S-DES2 exhibited the most pronounced enhancement in all three performance metrics. In summary, the orthogonal optimization strategy effectively drove the morphological evolution of FOX-7 toward a lower aspect ratio, and IGMH and interaction energy calculations provided direct evidence for solvent–solute interactions. The two natural deep eutectic solvent systems combine feasibility and environmental friendliness, offering a new pathway for the green crystallization processing of energetic materials. Download: Download high-res image (188KB) Download: Download full-size image