Dual Transient Networks of Polymer and Micellar Chains: Structure and Viscoelastic Synergy.

Sébastien Roland,Olga E Philippova,Andrey V Shibaev,Anna L Aleshina,Guillaume Miquelard-Garnier,Olga Matsarskaia,Ilias Iliopoulos,Cyrille Sollogoub,Alexis Chennevière

doi:10.3390/polym13234255

Abstract

Dual transient networks were prepared by mixing highly charged long wormlike micelles of surfactants with polysaccharide chains of hydroxypropyl guar above the entanglement concentration for each of the components. The wormlike micelles were composed of two oppositely charged surfactants potassium oleate and n-octyltrimethylammonium bromide with a large excess of anionic surfactant. The system is macroscopically homogeneous over a wide range of polymer and surfactant concentrations, which is attributed to a stabilizing effect of surfactants counterions that try to occupy as much volume as possible in order to gain in translational entropy. At the same time, by small-angle neutron scattering (SANS) combined with ultrasmall-angle neutron scattering (USANS), a microphase separation with the formation of polymer-rich and surfactant-rich domains was detected. Rheological studies in the linear viscoelastic regime revealed a synergistic 180-fold enhancement of viscosity and 65-fold increase of the longest relaxation time in comparison with the individual components. This effect was attributed to the local increase in concentration of both components trying to avoid contact with each other, which makes the micelles longer and increases the number of intermicellar and interpolymer entanglements. The enhanced rheological properties of this novel system based on industrially important polymer hold great potential for applications in personal care products, oil recovery and many other fields.

Highlights

Viscoelastic surfactants are able to self-assemble into very long wormlike micelles (WLMs) [1,2,3]
Binary transient networks composed of a network of entangled long wormlike surfactant micelles and a network of entangled polysaccharide chains were prepared
The WLMs forming the micellar network were composed of a mixture of anionic and cationic (C8TAB) surfactants with a large excess of anionic surfactant, that is they were highly negatively charged

Summary

Introduction

Viscoelastic surfactants are able to self-assemble into very long wormlike micelles (WLMs) [1,2,3]. Since WLMs are “living” objects that continuously break and reassemble, they change their structure to adapt to the variation of the external conditions This makes their viscoelastic properties tunable by many triggers including temperature, shear, and different additives [4,5,6,7,8]. The addition of hydrophobically modified guar to WLMs of cationic surfactant erucyl bis(hydroxyethyl)methylammonium chloride was shown to increase the viscosity by few orders of magnitude [14]. This effect was attributed to cross-linking of the WLMs by polymer through intercalation of its hydrophobic side groups into the micellar core

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