Mechanical annealing and memories in a disordered solid

Abstract

Shearing a disordered or amorphous solid for many cycles with a constant strain amplitude can anneal it, relaxing a sample to a steady state that encodes a memory of that amplitude. This steady state also features a remarkable stability to amplitude variations that allows one to read the memory. Here, we shed light on both annealing and memory by considering how to mechanically anneal a sample to have as little memory content as possible. In experiments, we show that a “ring-down” protocol reaches a comparable steady state but with no discernible memories and minimal structural anisotropy. We introduce a method to characterize the population of rearrangements within a sample and show how it connects with the response to amplitude variation and the size of annealing steps. These techniques can be generalized to other forms of glassy matter and a wide array of disordered solids, especially those that yield by flowing homogeneously.

Heterogeneous Dynamics of Sheared Particle-Laden Fluid Interfaces with Janus Particle Doping

“…PS spheres outside clusters show the largest nonaffine deformation, whereas Janus particles within clusters have the smallest nonaffine deformation. This difference is also apparent when comparing to previously studied undoped interfaces with bidisperse and monodisperse particles, , where the mean D min 2 at imposed stretching γ 0 /2 = 0.05 would be ∼0.01roughly half of the corresponding measurement outside clusters in the present study.…”

“…The analysis of nonaffine motion via D min 2 was originally invented by Falk and Langer for quantifying the viscoplastic deformation of amorphous solids 54 and has been employed previously in analyzing the dynamics of homogeneous particle monolayers. 50,55,56 Local Stretching. We first focus on the local stretching S(t) experienced by individual particles, a key quantity characterizing particle dynamics under shear and determining the shear moduli of the interface.…”

“…The minimum of D 2 , D min 2 , characterizes the local deviation of the particle dynamics from affine deformation. The analysis of nonaffine motion via D min 2 was originally invented by Falk and Langer for quantifying the viscoplastic deformation of amorphous solids and has been employed previously in analyzing the dynamics of homogeneous particle monolayers. ,, …”

“…Independent of the class of particles, the degree of nonaffine deformation shows a nonlinear increase with increasing γ 0 . Larger strains generally result in stronger nonaffine deformation. ,,, Similar to the local stretching, the nonaffine deformation is also heterogeneous. PS spheres outside clusters show the largest nonaffine deformation, whereas Janus particles within clusters have the smallest nonaffine deformation.…”

“…Without Janus particles, PS spheres alone form hexagonal crystals at the fluid interface due to the interparticle repulsion induced by the electric dipoles of particles at the interface ,− (Figure S4). The metallic surface of Janus particles modifies the charge distribution on the particles and lowers the strength of electric dipoles (Figure S4b), which therefore reduces the repulsion between Janus particles and PS spheres.…”