Mechanochemical perspective beyond thermochemical models: Desensitization mechanisms of CL-20 host-guest systems under shock loading

Experimental host-guest strategies improve the safety of the high-energy explosive CL-20 without compromising its energy output. However, the molecular mechanism underlying this improvement remains unclear. By systematic molecular simulations, this study provides novel mechanochemical insights into the basis of such safety-enhancing strategy. The results showed that under dynamic shock loading, CL-20 undergo significant intramolecular deformation, which accelerates chemical processes and accounts for its high mechanical sensitivity. Introducing guest molecules such as CO₂, N₂O, and H₂O inhibit this deformation, thereby altering decomposition pathways and reducing reaction rates. The calculated initial decomposition rate constants follow the order: ε-CL-20 (7.905 ps⁻¹) > CL-20/HMX (4.983 ps⁻¹) > CL-20/H₂O (4.597 ps⁻¹) > CL-20/N₂O (4.435 ps⁻¹) > CL-20/CO₂ (4.430 ps⁻¹) > 2000 K pyrolysis (1.465 ps⁻¹), which aligns well with the impact sensitivity ranking of CL-20-based supramolecular explosives. Further analysis reveals that asymmetric dihedral angle distortions in CL-20 lower the activation barrier for decomposition. Specifically, molecular twists exceeding 15° from the equilibrium reduce the activation energy by 20 kJ/mol. This investigation integrates physical deformation and chemical reactivity under dynamic mechanical stimuli, offering a novel mechanochemical perspective that overcomes the limitations of conventional thermochemical models. These findings not only unveil the molecular basis for desensitization of CL-20 host-guest explosives but also provide key theoretical insights for rationally designing next-generation energetic materials with tailored sensitivity.