How does a thermal binary crystal break under shear?

Abstract

When exposed to strong shearing, the particles in a crystal will rearrange and ultimately, the crystal will break by forming large nonaffine defects. Even for the initial stage of this process, only little effort has been devoted to the understanding of the breaking process on the scale of the individual particle size for thermalized mixed crystals. Here, we explore the shear-induced breaking for an equimolar two-dimensional binary model crystal with a high interaction asymmetry between the two different species such that the initial crystal has an intersecting square sublattice of the two constituents. Using Brownian dynamics computer simulations, we show that the combination of shear and thermal fluctuations leads to a characteristic hierarchical breaking scenario where initially, the more strongly coupled particles are thermally distorted, paving the way for the weakly coupled particles to escape from their cage. This in turn leads to mobile defects which may finally merge, proliferating a cascade of defects, which triggers the final breakage of the crystal. This scenario is in marked contrast to the breakage of one-component crystals close to melting. Moreover, we explore the orientational dependence of the initial shear direction relative to the crystal orientation and compare this to the usual melting scenario without shear. Our results are verifiable in real-space experiments of superparamagnetic colloidal mixtures at a pending air-water interface in an external magnetic field where the shear can be induced by an external laser field.

2D Stokesian Approach to Modeling Flow Induced Deformation of Particle Laden Interfaces

“…The above work was accomplished using a new 2D Stokesian simulation methodology that correlates interparticle interactions with the interfacial colloidal microstructure deformation due to surface flow for monodispersed charged microparticles at a fluid–fluid interface. In this methodology, interparticle interactions at fluid–fluid interfaces have been assumed to stem from dipolar repulsion between interfacial particles as well as capillary attraction caused by interfacial deformations, which differs significantly from the bulk of the literature which uses various repulsive or LJ potentials. , Furthermore, using 2D Stokesian dynamics, an underlying flow can be subjected to the entire interface, rather than through movement of the walls alone. , Therefore, this simulation methodology is applicable to capturing particle movements and microstructural formations and deformations at fluid–fluid interfaces subjected to different known flow fields.…”

Dynamical solid–liquid transition through oscillatory shear

“…The results on the single-component Lennard-Jones crystal motivate us to consider a system less prone to re-crystallization. Pre- vious studies on glass-forming systems have shown that a nonadditive 2:1 mixture of large and small Lennard-Jones particles is highly stable to crystallization 14 , probably due, firstly, to the vicinity of its stoichiometry to the eutectic point of the mixture 31 and secondly to the fact that binary crystals fail differently under shear compared to one-component crystals 32 . The mixture crystallizes into the Al 2 Cu arrangement, whose unit cell is characterized by spindles of small particles surrounded by square rings of large particles, forming a bicapped square antiprism 33 .…”

Dynamical modes of sheared confined microscale matter

“…Further, the material response to shear is intimately connected to the nonequilibrium dynamics of the constituent elements, that have been the subject of recent research with non-Brownian particles, 13,14 polymer-, 15 active bacteria-, 16 and colloidal suspensions in amorphous, [17][18][19] fluid-, 20,21 as well as crystalline states. [22][23][24][25] Colloidal suspensions under external fields have proven to be a powerful test bed system, that is used to study the role of channel geometry 9,17,26 hydrodynamic interactions, 24,27 frictional interparticle contact and lubrication, 28,29 as well as plastic events, [30][31][32] to cite a few. Key advantages of using colloidal particles are the possibilities to directly visualize the particle dynamics via video microscopy, and to tune the pair interactions using external fields.…”