Energetic molecules encapsulated inside carbon nanotubes and between graphene layers: DFT calculations

Insensitive energetic materials are desirable for propellants because of the reduced risks involved with their use. The ability to control the decomposition pathways for such materials is also of interest since it leads to optimal performance and controlled energy release. With these goals in mind, molecular structure and total energy calculations are used to investigate the confinement of energetic molecules inside carbon nanostructures. The molecules considered were FOX-7 (1,1-diamino-2,2-dinitroethylene), RDX (hexahydro-1,3,5-trinitro-striazine), HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine), DHT (3,6-di(hydrazino)-1,2,4,5-tetrazine), DiAT (3,6-diazido-1,2,4,5-tetrazine), DAAT (3,3′-azo-bis(6-amino-1,2,4,5- tetrazine)), and five different N-oxides of DAAT (DAATO_n, with n = 1-5). Each of the eleven molecules is encapsulated inside a carbon nanotube (CNT) in order to determine if it is stabilized from such confinement. The calculations predict that each molecule could be stabilized by 32-53 kcal/mol if a CNT of appropriate size is used. FOX-7, RDX, and HMX were also confined between graphene layers, resulting in these molecules being stabilized by 28-40 kcal/mol. The stabilization stems from dispersion interactions between the molecules and carbon nanostructures, Coulombic interactions due to charge transfer, and intermolecular H-bonding in some cases. Overall, each molecule can be stabilized when encapsulated in a carbon nanostructure of appropriate size, thereby reducing its sensitivity.