Stimuli-Responsive Polymers for Engineered Emulsions.

Emulsions are complex. Dispersing two immiscible phases, thus expanding an interface, requires effort to achieve and the resultant dispersion is thermodynamically unstable, driving the system toward coalescence. Furthermore, physical instabilities, including creaming, arise due to the presence of dispersed droplets of different densities to a continuous phase. Emulsions allow the formulation of oils, can act as vehicles to solubilise both hydrophilic and lipophilic molecules, and can be tailored to desirable rheological profiles, including "gel-like" behaviour and shear thinning. The usefulness of emulsions can be further expanded by imparting stimuli-responsive or "smart" behaviours by the inclusion of a stimuli-responsive emulsifier, polymer or surfactant. This enables manipulation like gelation, breaking, or aggregation, by external triggers such as pH, temperature, or salt concentration changes. This platform generates functional materials for pharmaceuticals, cosmetics, oil recovery, and colloid engineering, combining both smart behaviours and intrinsic benefit of emulsions. However, with increased functionality comes greater complexity. This review focuses on the use of stimuli-responsive polymers for the generation of smart emulsions, motivated by the great adaptability of polymers for this application and their efficacy as steric stabilisers. Stimuli-responsive emulsions are described according to the trigger used to provide the reader with an overview of progress in this field. This article is protected by copyright. All rights reserved.