Sharp symmetry-change marks the mechanical failure transition of glasses.

Dmitry V Denisov,Alessio Zaccone,Alessio Zaccone,Minh Triet Dang,P Schall,Bernd Struth,Gerard H Wegdam

doi:10.1038/srep14359

Abstract

Glasses acquire their solid-like properties by cooling from the supercooled liquid via a continuous transition known as the glass transition. Recent research on soft glasses indicates that besides temperature, another route to liquify glasses is by application of stress that drives relaxation and flow. Here, we show that unlike the continuous glass transition, the failure of glasses to applied stress occurs by a sharp symmetry change that reminds of first-order equilibrium transitions. Using simultaneous x-ray scattering during the oscillatory rheology of a colloidal glass, we identify a sharp symmetry change from anisotropic solid to isotropic liquid structure at the crossing of the storage and loss moduli. Concomitantly, intensity fluctuations sharply acquire Gaussian distributions characteristic of liquids. Our observations and theoretical framework identify mechanical failure as a sharp atomic affine-to-nonaffine transition, providing a new conceptual paradigm of the oscillatory yielding of this technologically important class of materials, and offering new perspectives on the glass transition.

Highlights

−1 2π (d) cages formed by their nearest neighbors allowing only for very slow structural rearrangements and leading to glass-like properties such as slow relaxation and aging[14]
The abrupt change of structural symmetry and nature of fluctuations consistently demonstrate a sharp transition in the microscopic degrees of freedom of a glass under the increasing oscillatory strain
The shear-induced, discrete symmetry characteristic of elastic solids vanishes abruptly, and isotropic Gaussian fluctuations characteristic of liquids appear, indicating a surprisingly sharp, dynamically-induced transition from a solid to a liquid-like state. This sharp transition and symmetry-breaking are all hallmarks of first-order like transitions

Summary

Introduction

−1 2π (d) cages formed by their nearest neighbors allowing only for very slow structural rearrangements and leading to glass-like properties such as slow relaxation and aging[14]. First-order transitions in solids imply a change of an underlying symmetry controlling the jump of the order parameter which so far remains elusive We resolve this controversy and provide the first experimental evidence that the stress-induced failure of glasses proceeds via a sharp symmetry change in the microscopic degrees of freedom of the glass. The transition occurs when affine and non-affine displacements reach, respectively, 4 and 0.8% of the average particle distance; the material reduces strain energies by sharply releasing some of the affine elastic strain into non-affine displacements. We show that this is likewise reflected in a sharp transition from correlated to uncorrelated (Gaussian) intensity fluctuations, confirming the sharp nature of the transition. We show that in glasses, the discrete-like anisotropic symmetry is entirely a result of the imposed deformation field

Methods

Results

Conclusion