Molecular simulation studies on the design of energetic ammonium dinitramide co-crystals for tuning hygroscopicity

Cocrystallization technology is an effective method for improving crystal properties. Ammonium dinitramide (ADN) is an important component of propellants. However, the high hygroscopicity property of ADN limits its applications. In order to solve this problem, nine energetic co-formers containing 2,4,5,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), benzotrifuroxan (BTF), 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX), 2,4,6-trinitrotoluene (TNT), butane-1,2,3,4-tetrayl tetranitrate (ETN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 1,3,5-trinitrobenzene (TNB), 2,4,6-trinitro-N-methylaniline (MATNB), and 1,3,3- trinitroazetidine (TNAZ) were selected to predict the hygroscopicity of co-crystals with the molar ratio of ADN to co-former as 1:1. A novel computational method has been put forward to select co-formers efficiently for designing energetic co-crystals with a low water sorption capacity. Based on the molecular electrostatic potential calculations, the intermolecular binding sites in the co-formers of co-crystal were found. By the lattice energy minimization methodology, the possible crystal structures were constructed, and the density and H-bond energy of possible energetic co-crystals were predicted. The co-crystal screening method was used to calculate pairwise interactions and select promising co-crystal formers for the experimental screening. This method can be used to predict the co-crystal hygroscopicity, which thus may speed up the progress of developing novel energetic co-crystal materials.