Pushing the glass transition towards random close packing using self-propelled hard spheres

Area of Science:

• Physics
• Materials Science
• Statistical Mechanics

Background:

• The concept of random close packing (RCP) for hard spheres, with a packing fraction near 0.64, has been debated for decades.
• Achieving high packing fractions beyond the glass transition (~0.58) is difficult due to non-equilibrium dynamics and diverging relaxation times.

Purpose of the Study:

• To investigate dense sphere packings and the glass transition in systems of hard particles.
• To explore methods for accessing states near random close packing.

Main Methods:

• Simulations of self-propelled hard spheres were performed.
• The effect of increasing particle activity on relaxation dynamics and glass transition was analyzed.

Main Results:

• Increasing particle activity significantly accelerates relaxation dynamics, by orders of magnitude.
• The glass transition shifts to higher packing fractions with increased activity.
• Fluid-like dynamics were observed at packing fractions approaching random close packing.

Conclusions:

• Self-propelled particles provide a route to study dense packings and the glass transition.
• This approach allows investigation of systems previously inaccessible due to slow dynamics.