Linear viscoelasticity of entangled wormlike micelles bridged by telechelic polymers : an experimental model for a double transient network

TL;DR

This study investigates the linear viscoelastic properties of a novel transient network formed by bridged wormlike micelles connected with telechelic polymers, revealing a two-mode Maxwell behavior and the relationship between network structure and viscoelasticity.

Contribution

It introduces a new experimental model of a double transient network with distinct viscoelastic modes, and provides insights into the relationship between network architecture and mechanical properties.

Findings

Bridged wormlike micelles exhibit two Maxwell modes with different timescales.

The fast mode correlates with the network of active bridging chains.

The slow mode relates to the entangled wormlike micelle network.

Abstract

We survey the linear viscoelasticity of a new type of transient network: bridged wormlike micelles, whose structure has been characterized recently [Ramos and Ligoure, (2007)]. This composite material is obtained by adding telechelic copolymers (water-soluble chains with hydrophobic stickers at each extremity) to a solution of entangled wormlike micelles (WM). For comparison, naked WM and WM decorated by amphiphilic copolymers are also investigated. While these latter systems exhibit almost a same single ideal Maxwell behavior, solutions of bridged WM can be described as two Maxwell fluids components blends, characterized by two markedly different characteristic times, t_fast and t_slow, and two elastic moduli, G_fast and G_slow, with G_fast >> G_slow. We show that the slow mode is related to the viscoelasticity of the transient network of entangled WM, and the fast mode to the network of telechelic active chains (i.e. chains that do not form loops but bridge two micelles). The dependence of the viscoelasticity with the surfactant concentration, phi, and the sticker-to-surfactant molar ratio, beta, is discussed. In particular, we show that G_fast is proportional to the number of active chains in the material, phi beta. Simple theoretical expectations allow then to evaluate the bridges/loops ratio for the telechelic polymers.