Mechanical Stability of 2D Ti2COx MXenes Under Compression Using Reactive Molecular Dynamics

TL;DR

This study uses reactive molecular dynamics to analyze the mechanical stability and buckling behavior of Ti2COx MXene nanosheets under various loads, revealing how surface chemistry and defects influence their failure modes.

Contribution

It provides new insights into the buckling and fracture mechanisms of Ti2COx MXenes, highlighting the effects of surface termination, defects, and confinement on their mechanical response.

Findings

Oxygen termination increases buckling stress from 1 GPa to 3.5 GPa.

Ti2CO2 nanosheets fracture at large strains, while Ti2C remain intact beyond 0.35 strain.

Buckling behavior varies with load direction and is affected by surface chemistry and defects.

Abstract

The compressive and post-buckling behavior of Ti2C and Ti2CO2 MXene nanosheets is studied using large-scale reactive molecular dynamics simulations. Nanosheets are subjected to uniaxial, biaxial, and shear loads to investigate their buckling modes, atomic-level deformation mechanisms, and failure characteristics. The results indicate that classical continuum mechanics significantly overestimates the buckling strains. Nanosheets exhibit higher resistance to buckling along the armchair direction than along the zigzag direction. Although atomic-scale defects reduce the buckling stress, they influence deformation only locally and do not alter the global buckling mode shapes. Lateral confinement pressure, such as that caused by polymerization-induced shrinkage in MXene-polymer composites, substantially increases the buckling stress. Oxygen surface termination increases the buckling stress from approximately 1 GPa to 3.5 GPa and reduces directional anisotropy in the elastic response. Under large compressive strains, Ti2CO2 nanosheets fracture, whereas Ti2C nanosheets retain structural integrity at strains exceeding 0.35. Atomistic analysis reveals opposite stress states in the top and bottom Ti layers due to curvature-induced strain gradients. Under biaxial compression, the nanosheet buckles in a dome-like shape, whereas shear loads produce elliptical deflection modes. The presented findings stimulate future studies on MXene morphological transformations, such as the development of nanotube, nanoscroll, and folded architectures.