Nanoemulsions hold vast potential for the engineering of advanced pharmaceuticals, foods and consumer products, and nanomaterials. However, they also exhibit thermodynamic and flow properties that are distinctly different from their larger counterparts, presenting challenges to their design and formulation. We seek to develop engineering principles by which the colloidal and rheological behavior of nanoemulsions can be rationally controlled, and use these principles to develop novel materials that harness their unique properties. This seminar will outline several efforts currentlyunderway in our group toward these aims.
First, we report the discovery of a new class nanoemulsions which can spontaneously form “organohydrogels”, viscoelastic solids containing up to 90% oil and water. This behavior is mediated by a thermoresponsive polymer gelator in the water phase, where the polymer chemistry provides a convenient method to control gelation and ultimate gel properties. Characterization of the microstructure and interactions in these materials reveals two distinct modes of gelation – in one case, weak polymer-surfactant interactions lead to a transient polymer network physically crosslinked by droplets; in the other, strong polymer bridging of droplets leads to the formation of a fractal droplet network with arrested dynamics. We find that this behavior is uniquely imparted by the nanoscale nature of the droplets, resulting from the long-range interdroplet interactions mediated by the gelator.
More recently, we have explored how to utilize this unique self-assembly behavior to create soft nanocomposites with well-controlled microstructure and properties. Specifically, the use of crosslinkable gelators enables the formation of a polymer network in the aqueous phase, and thus direct encapsulation of the nanoemulsion. We find that not only can the self-assembled microstructure be retained upon crosslinking, but the resulting nanocomposite exhibits responsive behavior reminiscent of the nascent self-assembly process. This can be utilized, for example, to create soft nanocomposites with switchable optical and mechanical properties. Finally, we demonstrate how these composites could be used as a multi-functional material platform for pharmaceutical formulation and drug delivery.