Nonmonotonic concentration dependence of the self-diffusion coefficient of surfactants in wormlike micellar solutions

TL;DR

This study uses simulations to reveal how surfactant diffusion in wormlike micellar solutions varies nonmonotonically with concentration, driven by competing diffusion mechanisms influenced by micellar dynamics.

Contribution

The paper demonstrates, through simulations, the nonmonotonic concentration dependence of surfactant self-diffusion and identifies the underlying mechanisms involving micellar dynamics and diffusion contributions.

Findings

Self-diffusion coefficient shows nonmonotonic behavior with concentration.

Competition between micellar center-of-mass and surfactant diffusion explains the behavior.

Micellar dynamics and scission/recombination kinetics govern diffusion mechanisms.

Abstract

We investigate the concentration dependence of surfactant diffusion in wormlike micellar solutions using dissipative particle dynamics simulations. The simulations show that the self-diffusion coefficient of surfactants exhibits a nonmonotonic dependence on the surfactant concentration, as observed in previous experiments. We quantitatively reveal that this nonmonotonic behavior results from the competition between micellar center-of-mass diffusion and surfactant diffusion within micelles by decomposing the mean-square displacement of surfactants into the corresponding contributions. Furthermore, our detailed analyses demonstrate how the competition between the two diffusion mechanisms is governed by the aggregation number distribution, the dynamics of individual surfactants and micelles, and the kinetics of micellar scission and recombination.