Rolling of an elastomeric cylinder: a Marangoni like effect in solid

TL;DR

This paper demonstrates how an elastomeric micro-cylinder rolls on a solid surface due to asymmetric swelling and evaporation of a solvent, driven by a Marangoni-like effect related to curvature and temperature.

Contribution

It introduces a novel mechanism of solid rolling driven by inhomogeneous swelling and evaporation, with a derived scaling relation explaining the velocity dependence.

Findings

Rolling velocity increases linearly with curvature.

Velocity increases with substrate and ambient temperature.

A scaling relation accurately predicts the observed behavior.

Abstract

A soft, thin, elastomeric micro-cylinder is induced to roll on a solid substrate by releasing small quantity of a solvent. The solvent swells the cylinder asymmetrically at one side and evaporates out of it from where it is exposed to atmosphere. Because of inhomogeneous swelling, the cylinder bends but tends to straighten out following evaporation of the solvent. Balance of these two opposing effects induces the static state of the cylinder to eventually bifurcate to a dynamic state of rolling. Similar to marangoni effect in liquid, the rolling motion of cylinder is driven and sustained by the curvature of the cylinder. The rolling velocity increases linearly with curvature of the bent cylinder which ceases to locomote as the curvature diminishes below a threshold limit. Similar to marangoni effect, the rolling velocity increases also with temperature of the substrate and surroundings. A scaling relation derived for the rolling velocity captures all these observations.