Collective rearrangement at the onset of flow of a polycrystalline hexagonal columnar phase

TL;DR

This study investigates the transition to flow in polycrystalline hexagonal columnar phases, revealing a collective reorganization of crystallites at flow onset through rheology and X-ray scattering, akin to fracture in heterogeneous materials.

Contribution

It demonstrates that flow initiation involves a bulk reorganization of the material, confirmed by combined rheology and X-ray scattering experiments, highlighting collective crystallite reorientation.

Findings

Power law creep regime observed before fluidization.

Fluidization time scales with shear modulus and stress.

Collective crystallite reorientation at flow onset.

Abstract

Creep experiments on polycrystalline surfactant hexagonal columnar phases show a power law regime, followed by a drastic fluidization before reaching a final stationary flow. The scaling of the fluidization time with the shear modulus of the sample and stress applied suggests that the onset of flow involves a bulk reorganization of the material. This is confirmed by X-ray scattering under stress coupled to \textit{in situ} rheology experiments, which show a collective reorientation of all crystallites at the onset of flow. The analogy with the fracture of heterogeneous materials is discussed.