Chaos in a melting pot

TL;DR

This paper reports a new flow instability during the shear of a phase change material near its solid-fluid transition, showing a progression from oscillatory to chaotic flow with increasing crystal growth, supported by experiments and a simple model.

Contribution

It introduces a novel flow instability linked to crystallization near phase transition, combining experimental stability diagrams with a Landau-Ginzburg model to explain bifurcation behavior.

Findings

Flow bifurcation occurs near crystallization onset.

Increasing temperature leads to chaotic flow.

Experimental and modeling results agree on bifurcation nature.

Abstract

A novel flow instability emerging during a rheometric flow of a phase change material sheared in the vicinity of the solid-fluid transition is reported. Right above the onset of the flow induced crystallisation, the presence of the crystals in the flow leads to a primary bifurcation towards an oscillatory flow state. A further decrease of the temperature beyond this point leads to an increase of the both the volume fraction and the size of the crystals which ultimately triggers a fully developed chaotic flow. A full stability diagram as a function of the imposed rate of deformation and the temperature is obtained experimentally. The experimental findings are complemented by a simple numerical toy model which, consistently with the experimental observations, indicates that the primary bifurcation is a second order bifurcation that can be accurately described by the stationary Landau-Ginzburg equation with a field.