Nanoindentation creep of supercrystalline nanocomposites

TL;DR

This study investigates the time-dependent creep behavior of supercrystalline nanocomposites using nanoindentation, revealing viscoelastic and viscoplastic effects influenced by organic crosslinking, and identifies deformation mechanisms at the organic interface scale.

Contribution

It provides the first detailed analysis of creep in supercrystalline nanocomposites, linking organic interface chemistry to mechanical deformation mechanisms.

Findings

Creep strains show partial recoverability, indicating viscoelasticity and viscoplasticity.

Crosslinking reduces overall deformability of the nanocomposites.

Deformation mechanisms are governed by organic ligand rearrangement at the nanoscale.

Abstract

Supercrystalline nanocomposites (SCNCs) are inorganic-organic hybrid materials with a unique periodic nanostructure, and as such they have been gaining growing attention for their intriguing functional properties and parallelisms with hierarchical biomaterials. Their mechanical behavior remains, however, poorly understood, even though its understanding and control are of paramount importance to allow SCNCs implementation into devices. An important aspect that has not been tackled yet is their time-dependent deformation behavior, which is nevertheless expected to play an important role in materials containing such a distribution of organic phase. Hereby, we report on the creep of ceramic-organic SCNCs with varying degrees of organic crosslinking, as assessed via nanoindentation. Creep strains and their partial recoverability are observed, hinting at the co-presence of viscoelasticity and viscoplasticity, and a clear effect of crosslinking in decreasing the overall material deformability. We rationalize our experimental observations with the analysis of stress exponent and activation volume, resulting in a power-law breakdown behavior and governing deformation mechanisms occurring at the organic sub-nm interfaces scale, in terms of organic ligands rearrangement. The set of results is reinforced by the evaluation of the strain rate sensitivity via strain rate jump tests, and the assessment of the effect of oscillations during continuous stiffness measurement mode.