Robust Scaling of Strength and Elastic Constants and Universal Cooperativity in Disordered Colloidal Micropillars

TL;DR

This study investigates the mechanical behavior of disordered colloidal micropillars, revealing a universal correlation between strength and elasticity and suggesting a common plastic deformation mechanism across disordered solids.

Contribution

It demonstrates a universal relationship between strength and elastic modulus in colloidal glasses and proposes a universal criterion for elastic-plastic transition in disordered materials.

Findings

Normalized strengths and elastic moduli vary over three orders of magnitude.

A robust, humidity-invariant correlation between strength and elastic modulus.

Characteristic strain for plastic events aligns with other disordered solids.

Abstract

We study the uniaxial compressive behavior of disordered colloidal free-standing micropillars composed of a bidisperse mixture of 3 and 6 um polystyrene particles. Mechanical annealing of confined pillars enables variation of the packing fraction across the phase space of colloidal glasses. The measured normalized strengths and elastic moduli of the annealed freestanding micropillars span almost three orders-of-magnitude despite similar plastic morphology governed by shear banding. We measure a robust correlation between ultimate strengths and elastic constants that is invariant to relative humidity, implying a critical strain of $\sim$0.01 that is strikingly similar to that observed in metallic glasses (MGs) [W.L. Johnson, K. Samwer, Phys. Rev. Lett. 95, 195501, 2005] and suggestive of a universal mode of cooperative plastic deformation. We estimate the characteristic strain of the underlying cooperative plastic event by considering the energy necessary to create an Eshelby-like ellipsoidal inclusion in an elastic matrix. We find that the characteristic strain is similar to that found in experiments and simulations of other disordered solids with distinct bonding and particle sizes, suggesting a universal criterion for the elastic to plastic transition in glassy materials with the capacity for finite plastic flow.