Multiscale Mechanical Response of 3D-Printed Diamondiynes: From Movable Interlocked Lattices to Architected Metamaterials

Diamondynes are a recently synthesized three-dimensional carbon allotrope, with interlocked and movable sublattices that introduce deformation modes not present in standard architected materials. Here, we report the first multiscale mechanical assessment of Diamondiyne-derived architectures by combining quasi-static compression of 3D-printed specimens with reactive molecular dynamics simulations of the corresponding atomic-scale models. We generate four geometries (3F, 2F-SY, 4F, and 2F-USY). All structures resulted in lower density in the range of 0.20-0.38 g.cm^-3. Experiments indicate that the symmetric two-sublattice structure (2F-SY) delivers the best performance, reaching a specific yield strength of 5.91 MPa.g^-1cm^-3 and a specific energy absorption of 279 J.g^-1, whereas 2F-USY architecture yielded the lowest values, with 0.77 MPa.g^-1.cm^-3 and 16 J.g^-1. The 4F geometry provided a specific energy absorption of 254 J.g^-1. The structures deformed through geometric collapse and strut buckling, which was due to diagonal shear in 2F-USY and progressive compaction in 2F-SY and 3F. Molecular dynamics simulations also confirmed these experimental trends and revealed strong directional anisotropy due to the arrangement of interlocked sublattices, with a stiffness of 24.1 GPa along the z-direction in the case of 4F architecture. Overall, Diamondiyne-derived architectures display geometry-dominated mechanical behavior and serve as a promising platform for lightweight, energy-absorbing metamaterials.

💡 Research Summary

This paper presents the first multiscale mechanical investigation of architectures derived from the newly synthesized three‑dimensional carbon allotrope known as Diamondyne. Diamondyne is distinguished by two interpenetrating carbon sublattices that can move relative to each other, providing deformation modes absent in conventional cellular metamaterials. Four distinct lattice topologies—3F (three interlocked sublattices), 2F‑SY (symmetrical two‑sublattice), 4F (four interlocked sublattices), and 2F‑USY (asymmetrical two‑sublattice)—were generated by geometrically scaling the atomic‑scale unit cells. The macroscopic specimens were fabricated using fused deposition modeling (FDM) with polylactic acid (PLA) filament, producing cubic samples of 15 mm, 20 mm, and 25 mm edge length, each printed in triplicate (total 36 specimens).

Quasi‑static uniaxial compression tests were performed on an Instron machine at a constant strain rate of 0.5 mm s⁻¹. Stress–strain curves were normalized by the measured densities (0.20–0.38 g cm⁻³) to obtain specific mechanical metrics: specific yield strength, specific resilience, and specific energy absorption. The symmetrical 2F‑SY lattice consistently outperformed the others, achieving a specific yield strength of 5.91 MPa·g⁻¹·cm³ and a specific energy absorption of 279 J·g⁻¹, with a prolonged plateau up to ~40 % strain. The 3F and 4F lattices displayed intermediate performance; the 4F architecture exhibited a pronounced directional stiffness of 24.1 GPa along the z‑axis, indicating strong anisotropy. In contrast, the asymmetrical 2F‑USY lattice showed the poorest results (0.77 MPa·g⁻¹·cm³, 16 J·g⁻¹) due to early diagonal shear and rapid densification.

Complementary reactive molecular dynamics (RMD) simulations were carried out with LAMMPS using the ReaxFF force field. Periodic cells of each lattice were equilibrated at 300 K and 1 atm for 200 ps (NPT ensemble) and then compressed uniaxially at a strain rate of 10⁻⁵ fs⁻¹ in the NVT ensemble. Simulations were performed along the x, y, and z directions to capture anisotropic behavior. The RMD results reproduced the experimental hierarchy: 2F‑SY showed the highest elastic modulus and a stable plateau, 4F displayed the highest stiffness along z, and 2F‑USY failed by early shear. Atomistic analysis revealed that failure mechanisms correspond to the macroscopic observations: diagonal shear dominates in 2F‑USY, while strut buckling and progressive compaction govern 2F‑SY and 3F.

The combined experimental‑computational study demonstrates that the mechanical response of Diamondyne‑derived metamaterials is geometry‑dominated. Symmetry and the number of interlocked sublattices enhance load redistribution, delay local instabilities, and increase energy‑absorbing capacity. Conversely, asymmetry introduces stress concentrations that precipitate early collapse. These findings suggest that Diamondyne lattices can serve as a versatile platform for lightweight, high‑energy‑absorption structures, with potential applications in aerospace, automotive crash protection, and protective gear.

Future work should explore the translation of these designs to actual carbon‑based Diamondyne (e.g., CVD‑grown) materials, high‑rate impact testing, and topology optimization using machine‑learning frameworks. Exploiting the intrinsic mobility of the sublattices could also enable reconfigurable or self‑healing metamaterials, expanding the functional envelope of architected carbon systems.