Static friction of liquid marbles

TL;DR

This paper investigates the static friction behavior of liquid marbles, revealing how their granular shell's geometry and density influence resistance to motion, and establishing them as a model for granular raft mechanics.

Contribution

It introduces the dependence of static friction on shell geometry and grain density, providing new insights into liquid marble mechanics and their relation to granular raft behavior.

Findings

Friction increases exponentially with grain density.

Friction depends on shell geometry.

Liquid marbles serve as a model for granular raft mechanics.

Abstract

Liquid marbles, droplets coated with a granular layer, are highly mobile as particles prevent capillary adhesion with the substrate. Yet, they exhibit static friction due to their granular shell, which resists rolling until it yields. This friction depends on the shell geometry and increases exponentially with grain density, indicating a logistic dependence of interparticle compressive forces on surface coverage, confirmed by yielding measurements in granular rafts. These results reveal the shell's dual role, and establish liquid marbles as a model system for probing granular raft mechanics.