Segregation by friction

TL;DR

This paper introduces a novel segregation mechanism in granular materials driven by differences in friction, demonstrated through experiments, modeling, and simulations, showing complete segregation under specific conditions.

Contribution

It presents the first experimental and simulation evidence of segregation caused solely by friction differences in granular materials.

Findings

Friction differences cause segregation in granular materials.

Segregation is enhanced with longer mean free paths.

A small hill in the container can achieve complete segregation.

Abstract

Granular materials are known to separate by size under a variety of circumstances. Experiments presented here and elucidated by modeling and MD simulation document a new segregation mechanism, namely segregation by friction. The experiments are carried out by placing steel spheres on a horizontal plane enclosed by rectangular sidewalls, and subjecting them to horizontal shaking. Half the spheres are highly smooth; the remainder are identical to the first half, except that their surfaces have been roughened by chemical etching, giving them higher coefficients of friction. Segregation due to this difference in friction occurs, particularly when the grains have a relatively long mean free path. In the presence of an appropriately chosen small ``hill'' in the middle of the container, the grains can be made to completely segregate by friction type.