Pseudomorphic Replacement Driven Construction of Hierarchical Homostructured CL-20 Core-Shell Architectures for Safety Improvement.

Hierarchical homostructured core-shell architectures (HHCS) integrate the advantages of maintaining high energy density and enhancing interfacial stability. However, their rational design and controllable construction remain significantly challenging. Herein, we propose a self-limiting surface pseudomorphic replacement strategy mediated by localized solvation regulation, enabling the precise construction of HHCS of ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-CL-20). Specifically, a γ-butyrolactone (γ-BL)/H2O mixed solvent system induces a selective surface dissolution-recrystallization process on ε-CL-20 crystals, forming a stable CL-20∙γ-BL solvate (Sγ-BL) layer. This layer undergoes interfacially induced nucleation on the crystal surface and exhibits self-limiting growth while preserving the morphology of the parent crystal, thereby enabling a morphology-preserving pseudomorphic replacement process. Upon thermal treatment, solvent removal and solid-state rearrangement facilitate the conversion of the outer solvate shell into the CL-20 phase, yielding a homogeneous shell with hierarchical nanoporous features. The resulting HHCS of CL-20 exhibits a remarkable enhancement in safety performance: its impact sensitivity value increases from 2.5 to 12 J, while the packing density decreases by only 4.85%. Importantly, the core-shell structure consists solely of ε-CL-20, with no heterogeneous materials. This work presents an interfacial-engineering strategy that provides new theoretical and methodological insights for the safety-oriented design and structural regulation of high-energy molecular crystals.