Relating Microstructure and Particle-level Stress in Colloidal Crystals Under Increased Confinement

TL;DR

This study investigates how confinement affects the microstructure and local stress distribution in colloidal crystals, revealing increased brittleness and localized stress patterns under compression.

Contribution

It introduces a combined imaging and stress measurement approach to link microstructure changes with particle-level stress in confined colloidal crystals.

Findings

Crystalline regions break into small domains with different packing.

Localized pressure and deviatoric stress are observed with shorter correlation lengths.

Mean deviatoric stress nearly doubles under confinement.

Abstract

The mechanical properties of crystalline materials can be substantially modified under confinement. Such modified macroscopic properties are usually governed by the altered microstructures and internal stress fields. Here, we use a parallel plate geometry to apply a quasi-static squeeze flow crushing a colloidal polycrystal while simultaneously imaging it with confocal microscopy. The confocal images are used to quantify the local structure order and, in conjunction with Stress Assessment from Local Structural Anisotropy (SALSA), determine the stress at the single-particle scale. We find that during compression, the crystalline regions break into small domains with different geometric packing. These domains are characterized by a pressure and deviatoric stress that are highly localized with correlation lengths that are half those found in bulk. Furthermore, the mean deviatoric stress almost doubles, suggesting a higher brittleness in the highly-confined samples.