Disordered Nanoparticle Packings under Local Stress Exhibit Avalanche-Like, Environmentally Dependent Plastic Deformation

Abstract

Nanoindentation experiments on disordered nanoparticle packings performed both in an atomic force microscope and in situ in a transmission electron microscope are used to investigate the mechanics of plastic deformation. Under an applied load, these highly porous films exhibit load drops, the magnitudes of which are consistent with an exponential population distribution. These load drops are attributed to local rearrangements of a small number of particles, which bear similarities to shear transformation zones and to the T1 process, both of which have been previously predicted for disordered packings. An increase in the relative humidity results in an increase in the number of observed load drops, indicating that the strength of the particle interactions has a significant effect on the modes of plastic deformation. These results suggest how disordered nanoparticle packings may be expected to behave in devices operating under varying environments.

Unraveling the Mechanisms Governing Anisotropy in Accordion‐Shaped Honeycomb Microlattice Fabricated by Two‐Photon Polymerization

“…Another notable feature is a large enclosed area between the loading and unloading segments of the force–displacement curve obtained from LD compression, which typifies large energy absorption. The net energy dissipated ( E diss ) during the test is the cyclic integral of the load–displacement curve, [ 30 ] which is the difference in the total work done during mechanical loading and the recovered elastic work during unloading [ 31 ] …”

Friction and Adhesion Govern Yielding of Disordered Nanoparticle Packings: A Multiscale Adhesive Discrete Element Method Study

“…This includes substantial particle-level spatial heterogeneity in stiffness, energy dissipation, and the amount of plasticity. This agreement is attained when using a value of adhesion several times greater than the van der Waals adhesion value for the nanoparticles, suggesting that stronger bonding mechanisms such as covalent bonds, hydrogen bonds, or capillary forces were present in the experiments. We have also shown that thermal activation can be omitted in our DNPs wherein strong dissipation exists, despite the fact that the constituent particles are nanoscale in size.…”

“…Subsequently, we altered interparticle interactions by introducing water vapor into the system, leading to the formation of liquid bridges between nanoparticles via capillary condensation. 12 Nevertheless, it is difficult to quantitatively determine how capillary bridges affect adhesion forces at this nanometer length scale. Therefore, this method is not a perfect analog for tuning adhesion.…”

“…The plasticity and flow of many classes of disordered packings have been investigated by experiments and simulations, including granular packings (typically with grains of >1 μm) such as sand, − pillars, − and disks , and those composed of smaller-scale constituents, including disordered nanoparticle packings (DNPs). − Studies have demonstrated that disordered packings across many size scales exhibit similar physics, such as localized constituent particle rearrangements, shear banding, and brittle fracture . Similar phenomena are also observed in many other amorphous materials, including metallic glasses − and colloidal glasses. , Despite these advances, the nature of these localized constituent-level rearrangements is still a rapidly developing area, with many unanswered questions.…”

“…Inspired by the unique experiments described above, , here we develop a novel multiscale adhesive discrete element method (MADEM) to simulate silica DNPs under single nanoparticle-level indentation. The MADEM simulations enable full resolution of each particle’s position, with complete tunability of interparticle friction and adhesion along with many other desired parameters, which is challenging or impossible to accomplish experimentally.…”