Department of Engineering Science, University of Oxford, Oxford, UK.
School of Engineering, University of Birmingham, Edgbaston, Birmingham, UK.
Nat Mater. 2021 Jul;20(7):1015-1023. doi: 10.1038/s41563-021-00977-6. Epub 2021 Apr 22.
Optimal mechanical impact absorbers are reusable and exhibit high specific energy absorption. The forced intrusion of liquid water in hydrophobic nanoporous materials, such as zeolitic imidazolate frameworks (ZIFs), presents an attractive pathway to engineer such systems. However, to harness their full potential, it is crucial to understand the underlying water intrusion and extrusion mechanisms under realistic, high-rate deformation conditions. Here, we report a critical increase of the energy absorption capacity of confined water-ZIF systems at elevated strain rates. Starting from ZIF-8 as proof-of-concept, we demonstrate that this attractive rate dependence is generally applicable to cage-type ZIFs but disappears for channel-containing zeolites. Molecular simulations reveal that this phenomenon originates from the intrinsic nanosecond timescale needed for critical-sized water clusters to nucleate inside the nanocages, expediting water transport through the framework. Harnessing this fundamental understanding, design rules are formulated to construct effective, tailorable and reusable impact energy absorbers for challenging new applications.
最优的机械冲击吸收器是可重复使用的，并具有较高的比能量吸收能力。在疏水性纳米多孔材料（如沸石咪唑酯骨架（ZIFs））中强制侵入液态水为设计此类系统提供了一种有吸引力的途径。然而，为了充分发挥其潜力，了解在实际的高应变率变形条件下的水侵入和挤出机制至关重要。在这里，我们报告了在升高的应变速率下受限水-ZIF 系统的能量吸收能力的显著增加。以 ZIF-8 作为概念验证，我们证明了这种有吸引力的速率依赖性通常适用于笼型 ZIFs，但对于含有通道的沸石则消失。分子模拟表明，这种现象源于在纳米笼内形成临界尺寸的水分子簇所需的固有纳秒时间尺度，从而加速了水在骨架中的传输。利用这一基本理解，制定了设计规则，以构建用于具有挑战性的新应用的有效、可定制和可重复使用的冲击能吸收器。
