Local shear transformations in deformed and quiescent hard-sphere colloidal glasses

Abstract

We performed a series of deformation experiments on a monodisperse, hard-sphere colloidal glass while simultaneously following the 3D trajectories of roughly 50,000 individual particles with a confocal microscope. In each experiment, we deformed the glass in pure shear at a constant strain rate (1 − 5 × 10 −5 s −1 ) to maximum macroscopic strains (5 − 10%), then reversed the deformation at the same rate to return to zero macroscopic strain. We also measured 3D particle trajectories in an identically-prepared quiescent glass in which the macroscopic strain was always zero. We find that shear transformation zones exist and are active in both sheared and quiescent colloidal glasses, revealed by a distinctive four-fold signature in spatial autocorrelations of the local shear strain.With increasing shear, the population of local shear transformations develops more quickly than in a quiescent glass, and many of these transformations are irreversible. When the macroscopic strain is reversed, we observe partial elastic recovery, followed by plastic deformation of the opposite sign, required to compensate for the irreversibly transformed regions. The average diameter of the shear transformation zones at maximum strain is 2.3 particle diameters.

Effects of cooling rate on particle rearrangement statistics: Rapidly cooled glasses are more ductile and less reversible

“…Though the linear stressstrain region in Fig. 1 is typically considered reversible, recent measurements have identified irreversible events and anelasticity on the micro-scale in this 'elastic' region [6,7,9,16,[19][20][21]]. …”

“…Several studies have suggested that amorphous solids do not possess a truly elastic response regime [6,7,9,16,[19][20][21]. For example, both a sublinear increase of stress versus strain (left inset to Fig.…”

“…Amorphous solids, including metallic, polymeric, and colloidal glasses, possess complex mechanical response to applied deformations, such as plastic flow [1][2][3][4], strain localization [5][6][7][8][9], creep flow [7,10,11], and fracture [12][13][14]. In crystalline materials, topological defects reflecting the symmetry of the crystalline phase govern response to deformation.…”

Stable small bubble clusters in two-dimensional foams

“…In contrast, it is much more difficult to identify the relevant defects that control the mechanical response in amorphous materials 1 . Disordered materials span a wide range of length scales from atomic systems, such as metallic glasses 2 and ceramics 3 , to colloidal suspensions 4,5 , and macroscopic particulate materials, such as foams [6][7][8][9] , emulsions 10 , and granular matter [11][12][13][14] .…”

Magnetic small-angle neutron scattering on bulk metallic glasses: A feasibility study for imaging displacement fields

“…The nature of these plastic events has been identified as isolated Eshelby quadrupoles that organize the nonaffine displacement field around a localized shear transformation. Indeed, the quadrupolar character of the displacement field has been verified experimentally by means of shear-deformation experiments on a monodisperse hard-sphere colloidal glass using confocal microscopy [8].…”