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

Abstract

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 (α-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.