The structural evolution of CL-20-based energetic host-guest solvates at decomposition temperature according to the perceptions of THz spectroscopy

Because of their unique physicochemical integration mode, energetic host-guest solvates provide a balanced method to expand CL-20 high explosives. CL-20/hydrogen peroxide (H2O2) energetic solvates maintain their detonation performance by combining H2O2 molecules into a lattice akin to hydrate CL-20/H2O solvate (alpha-CL-20). Herein, using periodic density functional theory (DFT) calculation and molecular dynamics simulation, the structural evolution and intermolecular interaction mechanism of orthorhombic CL-20/H2O2 (o-CL-20/H2O2), monoclinic CL-20/H2O2 (m-CL-20/H2O2) and CL-20/H2O solvates were monitored by the vibrational spectrum and vibrational density of states (VDOS) in the THz region when the temperature was increased from 298 K to 558 K. There was greater similarity in the vibrational characteristics of THz spectra for o-CL-20/H2O2 and CL-20/H2O solvates that was supported by the thermal expansion anisotropy of lattice parameters and that of difference for the m-CL-20/H2O2 solvate. With increased temperature, spectral signals in the power spectrum of VDOS reflected the conformational evolution of CL-20 molecules in o-CL-20/H2O2 solvate and structural insensitivity of m-CL-20/H2O2 solvate. THz peaks of CL-20/H2O revealed the weakening of intermolecular interactions of CL-20 and H2O molecules, which were in agreement with the fact that H2O molecules more easily escape from host-guest solvates, whereas the H2O2 molecule was restricted in a cage of CL-20 molecules for the m-CL-20/H2O2 solvate. RDF and hydrogen bond (H-bond) interaction analyses were performed to further clarify stronger intermolecular H-bond interactions in the o-CL-20/H2O2 solvate as compared to that of the other two combined with H2O2 or H2O solvates. This finding introduces new insights into clarifying the formation mechanism of hydroxide with CL-20-based energetic host-guest solvates. This work employed variable-temperature THz spectroscopy to analyze the structural evolution of host-guest energetic CL-20/H2O2 and CL-20/H2O solvates, as well as the mechanism of intermolecular interactions using DFT calculation and MD simulation.