Comparative Study of Experiments and Calculations on the Guest Molecules’ Escaping Mechanism of CL-20-Based Host–Guest Energetic Materials

CL-20-based host–guest energetic materials have high application value in the field of energetic materials. The phase-transition inhibition and stabilization mechanisms of CL-20-based host–guest energetic materials were revealed by combining experiments with molecular dynamics (MD) simulation. Based on the crystal structures, the super-cell models of host–guest energetic materials including CL-20/H2O, CL-20/H2O2, CL-20/N2O, and CL-20/CO2 were constructed. The phase transformation behavior and stability sequence of CL-20-based host–guest energetic materials were investigated using MD integrated with in situ powder X-ray diffraction (PXRD) and differential scanning calorimetry-thermogravimetry (DSC-TG) experiments. The escaping abilities of guest molecules from (002), (020), (021), (102), and (111) crystal faces of CL-20/H2O, CL-20/H2O2, CL-20/N2O, and CL-20/CO2 were evaluated using the target-MD method. It is proposed that the guest molecules could escape from the (002) crystal face more easily than the other faces. The escaping behaviors were studied using MD simulations. Based on the analysis of mean-square displacement (MSD), diffusion coefficients, and binding energies at different temperatures, the thermal stability order of the four CL-20-based host–guest materials was CL-20/CO2 > CL-20/N2O > CL-20/H2O2 > CL-20/H2O. This is consistent with experimental observations by in situ XRD and DSC analyses on these host–guest energetic materials. Meanwhile, by studying the escape paths of guest molecules, it was concluded that the escape method of guest molecules from a CL-20 crystal cell is "jumping" diffusion. By studying the MSD of host molecule CL-20 and the radial distribution function between the host molecule and the guest molecule, the structural stabilization mechanism of host–guest energetic materials was revealed. Our findings will help to reveal the solid-phase-transition inhibition mechanism of host–guest energetic materials and promote the development of host–guest explosives as smart materials.