Shockcompression of metal-organic frameworks*

To better protect personnel and equipment from injuries and damages caused by shock waves generated from explosions and high-speed impacts, we need improved methods to absorb shock waves and new methods to measure shock wave absorption. Metal-organic framework (MOF), a nanoporous crystalline material, caught our attention for its multiple responses to mechanical compressions and considerable mechanical energy absorbing capability in previous static high-pressure studies. In this work, we have developed a method to measure shock absorption using a laser-driven-flyer shock compression microscope and we have studied the shock wave absorption in MOF (denoted ZIF-8) films. We monitored the shock wave breaking out of the MOF films of different thicknesses with a photon-Doppler velocimeter (PDV). After shock we were able to collect the ZIF-8 films for post-mortem analysis.

We show that the ZIF-8 film absorbs 7 times more energy than an equivalent mass of PMMA. Our post-mortem electronic and Raman microscopy analyses reveal that the high efficiency of shock energy absorption in MOF film is resulted from the incorporation of multiple shock absorbing mechanisms, including crystal powder compaction, nanopore collapse, and endothermic bond breaking. The PDV data show that shock wave energy follows saturable absorption trend in MOFs. This study suggests new ways for fundamental shock investigations and illustrates how to improve the shock absorbing efficiency by engineering multiple shock absorbing mechanisms into armor materials.