The rise and fall of branching: a slowing down mechanism in relaxing wormlike micellar networks

TL;DR

This paper presents a mean-field kinetic model explaining the slow relaxation dynamics in wormlike micellar networks, highlighting the role of end-cap reduction and branching equilibrium, validated through simulations.

Contribution

It introduces a new kinetic model that captures the complex relaxation process involving end-cap reduction and branching in micellar networks, validated by molecular dynamics simulations.

Findings

Relaxation time scales exponentially with end-cap free energy.

Long relaxation times occur after thermal quenches and perturbations.

End-recombination dynamics may cause underestimation of viscoelastic time scales.

Abstract

A mean-field kinetic model suggests that the relaxation dynamics of wormlike micellar networks is a long and complex process due to the problem of reducing the number of free end-caps (or dangling ends) while also reaching an equilibrium level of branching after an earlier overgrowth. The model is validated against mesoscopic molecular dynamics simulations and is based on kinetic equations accounting for scission and synthesis processes of blobs of surfactants. A long relaxation time scale is reached both with thermal quenches and small perturbations of the system. The scaling of this relaxation time is exponential with the free energy of an end cap and with the branching free energy. We argue that the subtle end-recombination dynamics might yield effects that are difficult to detect in rheology experiments, with possible underestimates of the typical time scales of viscoelastic fluids.