  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
ex-trusion mechanisms under realistic, high-rate deformation conditions.
Herein, 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 depend-ence 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.
