Zhang Jidong, Guo Wei
International Center for Quantum Materials, School of Physics, Peking University, Beijing 100871, P. R. China.
Department of Physics, College of Science, Shihezi University, Shihezi 832003, PR China.
J Phys Chem A. 2022 Jan 20;126(2):286-295. doi: 10.1021/acs.jpca.1c09409. Epub 2022 Jan 5.
Host-guest inclusion, constructed by inserting small molecules into voids of energetic crystals, is a novel strategy for creating new energetic materials (EMs) with desired energy and safety. To provide an atomistic-level insight into the fact that small guest molecules can effectively regulate the stability and sensitivity of CL-20, we conducted ReaxFF-lg reactive molecular dynamics simulations on electric-field (EF)-induced decomposition of two typical host-guest EMs, CL-20/HO and CL-20/NO, and compared it to that of α-CL-20 and ε-CL-20. Our findings show that the sensitivity order of the CL-20-based EMs under EFs, α-CL-20/HO > ε-CL-20 > α-CL-20 > α-CL-20/NO, agrees well with the sensitivity obtained from the experiment (ε-CL-20 > α-CL-20 > α-CL-20/NO). Different effects of HO and NO molecules were found responsible for the distinct stability and sensitivity of these materials toward EFs. On the one hand, HO accelerate(s) the structural transformation of CL-20 and thus increases the sensitivity, because the wobbling NO group reduces the stability of CL-20 by weakening its adjacent C-N bonds, whereas NO makes this transition less likely, resulting in low sensitivity of α-CL-20/NO. On the other hand, HO and its decomposition intermediate OH radical can promote destruction of CL-20's cage structure and produce a large amount of water molecules to release heat, making CL-20/HO to decompose faster than ε-CL-20. NO molecules rarely react with CL-20 molecules but absorb heat from the surrounding decomposed CL-20 and thus slow down CL-20's decomposition, resulting in low sensitivity of α-CL-20/NO, as confirmed by transition-state calculations. The results provide a comprehensive understanding of the stability and sensitivity of CL-20-based host-guest explosives under EFs.
通过将小分子插入含能晶体的空隙中构建的主客体包合物，是一种用于制备具有所需能量和安全性的新型含能材料（EMs）的策略。为了从原子层面深入了解小分子能够有效调节CL-20的稳定性和感度这一事实，我们对两种典型的主客体EMs，即CL-20/HO和CL-20/NO，在电场（EF）诱导下的分解过程进行了ReaxFF-lg反应分子动力学模拟，并将其与α-CL-20和ε-CL-20的情况进行了比较。我们的研究结果表明，基于CL-20的EMs在电场作用下的感度顺序为α-CL-20/HO > ε-CL-20 > α-CL-20 > α-CL-20/NO，与实验得到的感度结果（ε-CL-20 > α-CL-20 > α-CL-20/NO）吻合良好。发现HO和NO分子的不同作用导致了这些材料对电场具有不同的稳定性和感度。一方面，HO加速了CL-20的结构转变，从而提高了感度，因为摆动的NO基团通过削弱其相邻的C-N键降低了CL-20的稳定性，而NO则使这种转变不太可能发生，导致α-CL-20/NO的感度较低。另一方面，HO及其分解中间体OH自由基能够促进CL-20笼状结构的破坏，并产生大量水分子以释放热量，使得CL-20/HO比ε-CL-20分解得更快。NO分子很少与CL-20分子反应，但从周围分解的CL-20吸收热量，从而减缓CL-20的分解，导致α-CL-20/NO的感度较低，过渡态计算证实了这一点。这些结果为基于CL-20的主客体炸药在电场作用下的稳定性和感度提供了全面的理解。
