Department of Chemistry and the Macromolecular Science and Engineering Program, University of Michigan, 930 North University Avenue, Ann Arbor, Michigan 48109-1055, United States.
U.S. Army Research Laboratory, FCDD-RLW-WB, Aberdeen Proving Ground, Maryland 21005, United States.
Acc Chem Res. 2021 Apr 6;54(7):1699-1710. doi: 10.1021/acs.accounts.0c00830. Epub 2021 Mar 16.
In spite of the importance of energetic materials to a broad range of military (munitions, missiles) and civilian (mining, space exploration) technologies, the introduction of new chemical entities in the field occurs at a very slow pace. This situation is understandable considering the stringent requirements for cost and safety that must be met for new chemical entities to be fielded. If existing manufacturing infrastructure could be leveraged, then this would offer a fundamental shift in the discovery paradigm. Cocrystallization is an approach poised to realize this goal because it can use existing materials and make new chemical compositions through the assembly of multiple unique components in the solid state. This account describes early proof-of-principle studies with widely used energetics in the field, including 2,4,6-trinitrotoluene (TNT) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), forming cocrystals with nonenergetic coformers that alter key properties such as density, sensitivity, and morphology. The evolution of these studies to produce cocrystals between two energetic components is detailed, including those exploiting new intermolecular interaction motifs that drive assembly such as halogen bonding. Implications of cocrystallization for performance, sensitivity to external stimuli, and manufacturability are explored at each stage. The derivation of many of these cocrystals from energetic materials in common use satisfies the goal of using materials already demonstrated to be cost-effective at scale and with well-understood safety profiles. The account concludes with a discussion of cocrystallizing molecules having excess of oxidizing power with those that are oxygen-deficient to push the limits of explosive performance to unprecedented levels. The purposeful production of an arbitrary combination of two solid components into a cocrystal is far from certain, but the studies described motivate the continued exploration of novel materials and the development of predictive models for identifying crystallization partners. When such cocrystals form, many of their most important properties cannot be predicted, pointing to another challenge for the purposeful development of energetic materials based on cocrystallization.
尽管能量材料对于广泛的军事（弹药、导弹）和民用（采矿、太空探索）技术至关重要，但在该领域引入新的化学实体的速度非常缓慢。考虑到新的化学实体必须满足成本和安全方面的严格要求，这种情况是可以理解的。如果能够利用现有的制造基础设施，那么这将是发现范式的根本转变。共晶是一种有望实现这一目标的方法，因为它可以利用现有材料，并通过在固态下组装多个独特的组件来制造新的化学成分。本说明描述了在该领域广泛使用的能量学的早期原理验证研究，包括 2,4,6-三硝基甲苯（TNT）和八氢-1,3,5,7-四硝基-1,3,5,7-四氮杂环辛烷（HMX），与改变密度、敏感性和形态等关键性质的非能量共晶形成共晶。详细介绍了这些研究从两种能量成分之间产生共晶的发展，包括利用新的分子间相互作用模式（如卤键）驱动组装的共晶。在每个阶段都探讨了共晶化对性能、对外界刺激的敏感性和可制造性的影响。这些共晶中的许多都是从常用的能量材料中衍生出来的，满足了使用已经证明在大规模生产中具有成本效益且安全性良好的材料的目标。本文以讨论具有过剩氧化能力的共晶化分子与缺氧分子相结合，将爆炸性能推向前所未有的水平结束。将两种固体成分任意组合成共晶的目的远非确定无疑，但所描述的研究激发了对新型材料的持续探索和识别结晶伙伴的预测模型的开发。当形成共晶时，它们的许多最重要的性质无法预测，这为基于共晶化的有目的的能量材料开发提出了另一个挑战。
