Rearrangement zone around a crack tip in a double self-assembled transient network

TL;DR

This paper explores how the structure and dynamics of self-assembled micellar networks influence crack nucleation and propagation, revealing a rearrangement zone whose size correlates with crack speed and ductility.

Contribution

It introduces the concept of a rearrangement zone around crack tips in double transient networks and links micelle alignment length scale to crack dynamics.

Findings

Rearrangement zone size increases with slower cracks.

Micelle alignment occurs over a finite length scale at the crack tip.

Double networks exhibit significant micelle rearrangements during cracking.

Abstract

We investigate the nucleation and propagation of cracks in self-assembled viscoelastic fluids, which are made of surfactant micelles reversibly linked by telechelic polymers. The morphology of the micelles can be continuously tuned, from spherical to rod-like to wormlike, thus producing transient double networks when the micelles are sufficiently long and entangled, and transient single networks otherwise. For a single network, we show that cracks nucleate when the sample deformation rate involved is comparable to the relaxation time scale of the network. For a double network, by contrast, significant rearrangements of the micelles occur as a crack nucleates and propagates. We show that birefringence develops at the crack tip over a finite length, $\xi$, which corresponds to the length scale over which micelles alignment occur. We find that $\xi$ is larger for slower cracks, suggesting an increase of ductility.