From crystal to amorphopus: a novel route towards unjamming in soft disk packings

TL;DR

This study explores how transforming a monodisperse crystal into bi- and polydisperse packings affects the unjamming transition, revealing that the critical packing fraction decreases and approaches random close packing due to particle size modifications.

Contribution

It introduces a novel numerical approach to study unjamming in soft disk packings by systematically modifying particle sizes from a crystalline state.

Findings

Critical packing fraction never exceeds initial crystal value

Lowest packing fraction approaches that of random close packing

Particle size modifications influence local order and contact networks

Abstract

It is presented a numerical study on the unjamming packing fraction of bi- and polydisperse disk packings, which are generated through compression of a monodisperse crystal. In bidisperse systems, a fraction f_+ = 40% up to 80% of the total number of particles have their radii increased by \Delta R, while the rest has their radii decreased by the same amount. Polydisperse packings are prepared by changing all particle radii according to a uniform distribution in the range [-\Delta R,\Delta R]. The results indicate that the critical packing fraction is never larger than the value for the initial monodisperse crystal, \phi = \pi/12, and that the lowest value achieved is approximately the one for random close packing. These results are seen as a consequence of the interplay between the increase in small-small particle contacts and the local crystalline order provided by the large-large particle contacts.