Organic Filling Mitigates Flaw-Sensitivity of Nanoscale Aragonite

Engineering
at nanoscale holds the promise of tuning materials
with extraordinary properties. However, macroscopic approaches commonly
used to predict mechanical properties do not fully apply at nanoscale
level. A controversial feature is the presence of nanoflaws in aragonite
nacre, as it is expected that flaws would weaken the material, whereas
nacre still shows high toughness and rupture strength. Here, we performed
molecular dynamics and finite element simulations emulating flaws
found in aragonite nacre. Our simulations reveal two regimes for fracture:
nacre remains flaw-insensitive only for flaws smaller than 1.2 nm
depth, or flaws of a few atoms, whereas larger flaws follow a Griffith-like
trend resembling macroscopic fracture. We tested an alternative mechanism
for flaw-insensitivity in nacre, and investigated the mechanical effect
of organic filling to mitigate fracture. We found that a single nacre
protein, perlucin, decreases the stress concentration at the fracture
point, producing enhancements of up to 15% in rupture strength. Our
study reveals a more comprehensive understanding of mechanical stability
at the nanoscale and offers new routes toward hybrid nanomaterials.