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

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.