# Unidirectional Ligament Orientation Enables Enhanced Out-of-Plane Mechanical Properties in Anisotropic Nanoporous Gold

## TL;DR

This paper introduces anisotropic nanoporous gold with unidirectional ligaments that improves mechanical strength and stiffness for engineering applications.

## Contribution

The novel contribution is the design of anisotropic nanoporous gold with unidirectional ligaments enhancing out-of-plane mechanical properties.

## Key findings

- ANPG shows higher out-of-plane Young’s modulus and yield strength than isotropic NPG.
- ANPG maintains toughness comparable to INPG at lower relative densities.
- ANPG exhibits a hybrid deformation mechanism with significant ligament stretching.

## Abstract

Nanoporous gold (NPG), characterized by a bicontinuous network of nanoscale solid ligaments and pore channels, exhibits exceptional physical and chemical properties. However, the limited strength and stiffness of traditional isotropic NPG (INPG) have constrained its engineering applications. To effectively enhance the mechanical properties of NPG, this work proposes an innovative anisotropic NPG (ANPG) architecture featuring unidirectional ligament orientation. By controlling spinodal decomposition parameters, ANPG models with preferentially aligned ligaments and INPG with random ligament orientation are constructed, spanning relative densities from 0.30 to 0.50. The ligament length and diameter of ANPG along the out-of-plane direction are twice those along other directions. Molecular dynamics simulations of tensile tests show that ANPG exhibits superior out-of-plane Young’s modulus and yield strength but reduced fracture strain compared to INPG. Crucially, ANPG maintains toughness comparable to INPG at relative densities below 0.4, offering an optimal strength-toughness balance for practical applications. Scaling law analysis demonstrates INPG follows classical bending-dominated Gibson-Ashby behavior, while ANPG exhibits a hybrid deformation mechanism with significant ligament stretching contribution. Atomic-scale analysis reveals that both structures develop dislocation-mediated plasticity initially, but ANPG transitions to localized ligament necking and fractures more rapidly, explaining its reduced ductility. Strain localization quantification, measured by atomic shear strain standard deviation, confirms the intensifier deformation concentration in ANPG at large plastic strain. These findings suggest anisotropic design as a powerful strategy for developing high-performance NPG for actuators, sensors, and catalytic systems where simultaneous mechanical robustness and functional performance are required.