Experimental Studies of the Jamming Behaviour of Triblock Copolymer Solutions and Triblock Copolymer-Anionic Surfactant Mixture

TL;DR

This study investigates how triblock copolymer solutions and their mixtures with anionic surfactants transition between jammed and unjammed states, revealing effects of concentration, micelle shape, and packing on their mechanical properties.

Contribution

It provides experimental insights into the microscopic dynamics and phase behaviour of copolymer-surfactant mixtures, highlighting the impact of aggregation and packing on jamming.

Findings

Increasing copolymer concentration raises the complex moduli.

Adding surfactant decreases the complex moduli significantly.

A phase diagram maps the jamming-unjamming transitions.

Abstract

Photon correlation spectroscopy and rheological measurements are performed to investigate the microscopic dynamics and mechanical responses of aqueous solutions of triblock copolymers and aqueous mixtures of triblock copolymers and anionic surfactants. Increasing the concentration of triblock copolymers results in a sharp increase in the magnitude of the complex moduli characterising the samples. This is understood in terms of the changes in the aggregation and packing behaviours of the copolymers and the constraints imposed upon their dynamics due to increased close packing. The addition of suitable quantities of an anionic surfactant to a strongly elastic copolymer solution results in a decrease in the complex moduli of the samples by several decades. It is argued that the shape anisotropy and size polydispersity of the micelles comprising mixtures cause dramatic changes in the packing behaviour, resulting in sample unjamming and the observed decrease in complex moduli. Finally, a phase diagram is constructed in the temperature-surfactant concentration plane to summarise the jamming-unjamming behaviour of aggregates constituting triblock copolymer-anionic surfactant mixtures.