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 havehigh applicationvalue in the field of energetic materials. The phase-transition inhibitionand stabilization mechanisms of CL-20-based host-guest energeticmaterials were revealed by combining experiments with molecular dynamics(MD) simulation. Based on the crystal structures, the super-cell modelsof 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 stabilitysequence of CL-20-based host-guest energetic materials wereinvestigated 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 proposedthat the guest molecules could escape from the (002) crystal facemore easily than the other faces. The escaping behaviors were studiedusing 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-guestmaterials was CL-20/CO2 > CL-20/N2O >CL-20/H2O2 > CL-20/H2O. This isconsistent withexperimental observations by in situ XRD and DSC analyses on thesehost-guest energetic materials. Meanwhile, by studying theescape paths of guest molecules, it was concluded that the escapemethod of guest molecules from a CL-20 crystal cell is "jumping"diffusion. By studying the MSD of host molecule CL-20 and the radialdistribution function between the host molecule and the guest molecule,the structural stabilization mechanism of host-guest energeticmaterials was revealed. Our findings will help to reveal the solid-phase-transitioninhibition mechanism of host-guest energetic materials andpromote the development of host-guest explosives as smart materials.