Polymer–surfactant complexation as a generic route to responsive viscoelastic nanoemulsions

Abstract

We present a new scheme for imparting thermoreversible viscoelasticity to oil-in-water nanoemulsions based on polymer–surfactant self-assembly in solution. Specifically, bridging of polymer-induced micelles in the aqueous phase give rise to a transient network of interdroplet bridges without compromising colloidal stability. Characterization of the structure, dynamics, and rheological properties over a broad range of material chemistries and compositions suggests rules for controlling the resulting viscoelasticity. Remarkably, the linear viscoelasticity of these systems exhibits time–temperature superposition, which is purely driven by dynamics without noticeable structure changes. This allows quantification of an activation energy for network formation, which is correlated with the viscoelastic properties across a number of parameters, including polymer and surfactant concentration as well as droplet size. However, a complex dependence of the activation energy on fluid composition distinguishes these novel viscoelastic nanoemulsions from other types of transient gels, and we reconcile their behaviour with established mechanisms of polymer–surfactant complexation.