Influence of friction on granular segregation

TL;DR

This study experimentally demonstrates that increasing particle friction causes a sharp transition from reverse Brazil Nut effect to the Brazil Nut effect in shaken granular mixtures, highlighting friction's role in segregation mechanisms.

Contribution

It reveals how particle friction influences granular segregation, showing a transition from RBNE to BNE with increased friction due to aging.

Findings

Friction increase causes a transition from RBNE to BNE.

Segregation behavior depends on particle aging and friction.

Convection and buoyancy compete in segregation dynamics.

Abstract

Vertical shaking of a mixture of small and large beads can lead to segregation where the large beads either accumulate at the top of the sample, the so called Brazil Nut effect (BNE), or at the bottom, the Reverse Brazil Nut effect (RBNE). Here we demonstrate experimentally a sharp transition from the RBNE to the BNE when the particle coefficient of friction increases due to aging of the particles. This result can be explained by the two competing mechanisms of buoyancy and sidewall-driven convection, where the latter is assumed to grow in strength with increasing friction.