Structural universality in disordered packings with size and shape polydispersity

Area of Science:

• Physics
• Materials Science
• Statistical Mechanics

Background:

• Disordered jammed packings are complex systems with applications in various fields.
• Understanding the structural properties of these packings, especially with polydispersity, is crucial.
• Previous studies focused on size polydispersity, but coupled size and shape effects are less understood.

Purpose of the Study:

• To numerically investigate disordered jammed packings with both size and shape polydispersity.
• To generalize the observation of denser packing by larger particles to systems with coupled shape dispersity.
• To establish a universal relationship between local compactness and particle size in polydisperse packings.

Main Methods:

• Numerical investigation of frictionless superellipsoidal particles.
• Implementation of set Voronoi tessellation to evaluate local specific volume.
• Definition of normalized free volume (vf) and normalized particle size (A) for compactness analysis.
• Consideration of three systems: mixed-shape, size-polydisperse, and coupled size-shape polydisperse packings.

Main Results:

• A universal relationship, vf(A), was found for size-polydisperse packings, independent of specific particle shapes or dispersity.
• This universality was validated using a mean-field approximation.
• For coupled size and shape polydispersity, the master curve vf(A) is preserved if particles have similar shape factors (αc); deviations occur when αc dispersity is high.

Conclusions:

• The study reveals a universal packing behavior (vf(A)) in disordered jammed packings with coupled size and shape polydispersity.
• The dispersity of particle shapes, quantified by αc, influences the deviation from this universal curve.
• Polydisperse packings can be understood as combinations of building blocks with a universal packing relation.