Avalanches, plasticity, and ordering in colloidal crystals under compression

Abstract

Using numerical simulations we examine colloids with a long-range Coulomb interaction confined in a two-dimensional trough potential undergoing dynamical compression. As the depth of the confining well is increased, the colloids move via elastic distortions interspersed with intermittent bursts or avalanches of plastic motion. In these avalanches, the colloids rearrange to minimize their colloid-colloid repulsive interaction energy by adopting an average lattice constant that is isotropic despite the anisotropic nature of the compression. The avalanches take the form of shear banding events that decrease or increase the structural order of the system. At larger compressions, the avalanches are associated with a reduction of the number of rows of colloids that fit within the confining potential, and between avalanches the colloids can exhibit partially crystalline or even smectic ordering. The colloid velocity distributions during the avalanches have a non-Gaussian form with power law tails and exponents that are consistent with those found for the velocity distributions of gliding dislocations. We observe similar behavior when we subsequently decompress the system, and find a partially hysteretic response reflecting the irreversibility of the plastic events.

Rearrangement of two dimensional aggregates of droplets under compression: Signatures of the energy landscape from crystal to glass

“…Clearly, for a p → (p − 1) transition, a crystal made of small droplets will fracture at a smaller spacing between the pipettes (trace 1), compared to a crystal of larger droplets (trace 7). All the bonds are broken in a catastrophic and coordinated manner, in agreement with other studies of crystals under compression [41,42].…”

Avalanche dynamics for active matter in heterogeneous media

“…Motion often occurs in avalanches close to the depinning transition, and if depinning is associated with critical features such as diverging characteristic lengths and times, the avalanches and other fluctuating quantities will exhibit broad or power law distributions [5,7]. Scale-free avalanche dynamics often appear near yielding or unjamming transitions, such as in the intermittent motion of dislocations in crystalline solids [9][10][11] or the rearrangements of particles at yielding in amorphous materials [12][13][14][15]. For loose assemblies of particles such as grains or bubbles, the shear modulus becomes finite above a density f j when a jamming transition occurs [16,17], and it is known that in such systems, the dynamics become increasingly intermittent as the jamming point is approached, producing power law distributions in a variety of dynamic quantities [18][19][20][21][22][23].…”

Ptychographic X‐Ray Imaging of Colloidal Crystals

“…The flexibility of colloidal crystals and their response to external stimuli along with their unique optical properties such as the strongly pronounced structural color and photonic band gap makes them attractive for many applications . Moreover, defects, which determine the mechanical properties of many engineering materials such as metals, can be studied with “atomic” resolution using colloidal crystals …”