Direct Evidence of Void-Induced Structural Relaxations in Colloidal Glass Formers

Abstract

Particle dynamics in supercooled liquids are often dominated by string-like motions in which lines of particles perform activated hops cooperatively. The structural features triggering these motions, crucial in understanding glassy dynamics, remain highly controversial. We experimentally study microscopic particle dynamics in colloidal glass formers at high packing fractions. With a small polydispersity leading to glass-crystal coexistence, a void in the form of a vacancy in the crystal can diffuse reversibly into the glass and further induces string-like motions. In the glass, a void takes the form of a quasi-void consisting of a few neighboring free volumes and is transported by the string-like motions it induces. In fully glassy systems with a large polydispersity, similar quasi-void actions are observed. The mobile particles cluster into string-like or compact geometries, but the compact ones can further be broken down into connected sequences of strings, establishing their general importance.

Diffusion coefficient power laws and defect-driven glassy dynamics in swap acceleration

“…A more informative illustration is provided by particle trajectories, where individual trajectories of groups of particles nicely connect to form strings (see SI). We observe striking resemblance of these strings to those in, for example, experimental glassy colloidal systems [20]. Unlike in realistic glass, string-like motions in our model can be trivially understood.…”

“…An important question is: are there analogous dynamics-dominating defects in realistic glasses? In close association with the freevolume theory, a major candidate is void or, more generally, a fragmented version called quasi-void, which has been recently identified in colloid experiments via a reversible transformation into a vacancy at a glass-crystal interface [20]. In this picture of void-induced dynamics, a particle hopping into a nearest-neighboring void, leaving another void behind, can be equivalently described as a local swap between a particle and a void.…”

Fragile Glasses Associated with a Dramatic Drop of Entropy under Supercooling

“…We assume a void-induced dynamics, which has been directly observed in recent experiments on glassy colloidal systems [36]. Using the Metropolis algorithm, each particle can hop to an unoccupied nearest neighbor site at temperature T at a rate…”

Emergence of two-level systems in glass formers: a kinetic Monte Carlo study

“…A close examination of the particle dynamics shows that stronger particle localization at low T accounts for both the glass transition and the emergence of TLS. In the DPLM, particle movements are induced by voids, a mechanism supported by recent colloidal experiments [23]. Since a particle hop can be equivalently considered as the opposite hop of a void, we describe the dynamics of particles and voids interchangeably.…”