Theoretical insight into the binding energy and detonation performance of ε-, γ-, β-CL-20 cocrystals with β-HMX, FOX-7, and DMF in different molar ratios, as well as electrostatic potential

Molecular dynamics method was employed to study the binding energies on the selected crystal planes of the epsilon-, gamma-, beta-conformation 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (epsilon-, gamma-, beta-CL-20) cocrystal explosives with 1,1-diamino-2,2-dinitroethylene (FOX-7), 1,3,5,7-tetranitro-1,3,5,7-tetrazacyclooctane with beta-conformation (beta-HMX) and N,N-dimethylformamide (DMF) in different molar ratios. The oxygen balance, density, detonation velocity, detonation pressure, and surface electrostatic potential were analyzed. The results indicate that the binding energies E-b* and stabilities are in the order of 1:1 > 2:1 > 3:1 > 5:1 > 8:1 (CL-20:FOX-7/beta-HMX/DMF). The values of E-b* and stabilities of the energetic-nonenergetic CL-20/DMF cocrystals are far larger than those of the energetic-energetic CL-20/FOX-7 and CL-20/beta-HMX, and those of CL-20/beta-HMX are the smallest. For CL-20/FOX-7 and CL-20/beta-HMX, the largest E-b* appears in the cocrystals with the 1:1, 1:2 or 1:3 molar ratio, and the stabilities of the cocrystals with the excess ratio of CL-20 are weaker than those in the cocrystals with the excess ratio of FOX-7 or beta-HMX. In CL-20/FOX-7, CL-20 prefers adopting the epsilon-form, and epsilon-CL-20 is the preference in CL-20/beta-HMX, and epsilon-CL-20 and beta-CL-20 can be found in CL-20/DMF. The CL-20/FOX-7 and CL20/beta-HMX cocrystals with low molar ratios can meet the requirements of low sensitive high energetic materials. Surface electrostatic potential reveals the nature of the sensitivity change upon the cocrystal formation.