Long-Range Strain Correlations in Sheared Colloidal Glasses

Van der Waals-Zeeman Institute, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
Physical Review Letters (Impact Factor: 7.51). 11/2011; 107(19):198303. DOI: 10.1103/PhysRevLett.107.198303
Source: PubMed


Glasses behave as solids on experimental time scales due to their slow relaxation. Growing dynamic length scales due to cooperative motion of particles are believed to be central to this slow response. For quiescent glasses, however, the size of the cooperatively rearranging regions has never been observed to exceed a few particle diameters, and the observation of long-range correlations has remained elusive. Here, we provide direct experimental evidence of long-range correlations during the deformation of a dense colloidal glass. By imposing an external stress, we force structural rearrangements, and we identify long-range correlations in the fluctuations of microscopic strain and elucidate their scaling and spatial symmetry. The applied shear induces a transition from homogeneous to inhomogeneous flow at a critical shear rate, and we investigate the role of strain correlations in this transition.

Download full-text


Available from: Bernard Nienhuis,
  • Source
    • "Recent experiments on soft glasses reveal long-range correlations in the microscopic flow of glasses [6] [7]. Such long-range correlations reflect a high susceptibility of the microscopic dynamics to the applied shear. "
    [Show abstract] [Hide abstract]
    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 forces relaxation and flow. Here we provide experimental evidence that the stress-induced onset of flow of glasses occurs via a sharp first order-like transition. 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 transition from the linear to the nonlinear regime. Concomitantly, intensity fluctuations sharply acquire liquid distributions. These observations identify the yielding of glasses to increasing stress as sharp affine-to-nonaffine transition, providing a new conceptual paradigm of the yielding of this technologically important class of materials, and offering new perspectives on the glass transition.
  • Source
    • "And, so far, there is no indication of any underlying macroscopic mechanical instability driving the formation of shear bands. While there have been several observations in experiments [20] [21], numerical simulations [22] [23] [24] [25] [26] [27] and phenomenological models [28] [29], a quantitative analysis that allows to predict the conditions under which shear bands form in glasses is lacking. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The response of glasses to mechanical loading often leads to the formation of inhomogeneous flow patterns that strongly affect materials properties. Among them, shear bands are ubiquitous in a wide variety of materials, ranging from soft matter systems to metallic alloys. Shear banding is associated with strain localization, i.e. the deformation of the sheared glassy solid is localized in space in form of band-like structures. These structures are often precursors to catastrophic failure, implying that a proper understanding of the underlying mechanisms could lead to the design of smarter materials. However, despite its importance in material science, the microscopic origin of shear banding in glassy materials is only poorly understood. Here, the formation of shear banding in glassy systems is revealed by non-equilibrium molecular dynamics simulations (NEMD) of a binary Lennard-Jones mixture, subject to a constant strain rate. In its glass state, this system exhibits for all considered strain rates the formation of a percolating cluster of mobile regions at a critical strain. We show that this percolation transition belongs to the universality class of directed percolation. Only at low shear rates, where the steady-state stress is close to the yielding threshold, the percolating cluster evolves into a transient (but long-lived) shear band with a diffusive growth of its width.
  • Source
    • "The fact that a common failure mode is observed in amorphous solids with very different characteristic length scales and inter-particle interactions has led to the proposal that the fundamental plastic event found in MGs may in fact be universal to all amorphous solids. Indeed, direct visualizations of sheared 3D colloid systems suggest cooperative shearing of collections of particles [13], [15], [16], although the link between these inelastic building blocks and macroscopic yielding is still not clear. "
    [Show abstract] [Hide abstract]
    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.
    Proceedings of the National Academy of Sciences 08/2014; 111(51). DOI:10.1073/pnas.1413900111 · 9.67 Impact Factor
Show more