Direct observation of stringlike collective motion in a two-dimensional driven granular fluid

Area of Science:

• Physics
• Materials Science
• Soft Matter Physics

Background:

• Polycrystalline materials form grains separated by grain boundaries (GBs).
• GB structure and dynamics significantly influence material properties, plastic deformation, and transport.
• Understanding particle motion within GBs is crucial for predicting material behavior.

Purpose of the Study:

• To experimentally investigate particle motion in the grain-boundary (GB) regions of a quasi-two-dimensional driven system of hard spheres.
• To explore the influence of adding small particles on collective motion within GBs.
• To compare experimental findings with molecular-dynamics simulations of polycrystalline materials.

Main Methods:

• Experimental investigation of particle motion in quasi-two-dimensional granular systems.
• Utilizing dense ensembles of monodisperse hard spheres.
• Introducing small particles to modulate collective motion.

Main Results:

• Particle motion in GB regions is characterized by highly cooperative, string-like dynamics.
• This motion is analogous to that observed in glass-forming liquids.
• The scale of collective motion can be modulated by the addition of smaller particles.

Conclusions:

• Grain boundaries in hard sphere systems exhibit collective particle motion similar to glass-forming liquids.
• The addition of small particles offers a method to control and modulate this collective motion.
• Findings align with simulations of metallic polycrystalline materials, suggesting broader applicability.