Engineered emulsions, polymer structured oils and responsive polymer nanoparticles via polymer design and emulsion templating

摘要

The synthesis of branched copolymers with precise composition, specifically the ratio of methacrylic acid (MAA) to ethylene glycol (EG) has been demonstrated. These polymers were used to stabilise dodecane oil-in-water emulsion droplets. It was demonstrated in the literature that branched copolymers containing a 1:1 ratio of MAA:EG formed pH-responsive emulsions, capable of triggered inter-droplet hydrogen bonding to form engineered emulsions (EE). The effect of varying this ratio on the rate of engineered emulsion formation, and the resulting strength and stiffness of the emulsion droplet aggregates was investigated. This control over systems is exemplified by the demonstration of selective acid-triggered assembly of binary mixtures of droplets stabilised by polymer containing only EG functionality with droplets stabilised by polymers containing only MAA functionality. EEs stabilised using a branched copolymer containing a 1:1 ratio of MAA:EG were produced and allowed to dehydrate, leading to the removal of water from droplet interstitial sites. The resulting single-phase materials are known as polymer-structured oils (PSOs), held structurally by the inter-droplet polymer-polymer interactions. These polymer boundaries provide enough of a barrier between droplets to prevent coalescence upon the removal of water, allowing reversible hydration of PSOs to reform EEs. The production of large volume, well-defined EEs produced via the hydrolysis of glucono-δ-lactone (GδL) to gluconic acid in an emulsion’s water phase was investigated. This process provides a homogeneous pH trigger for the formation of EEs, eliminating the slow diffusion of HCl. A homogeneous pH trigger also allows the formation of EEs to be studied in situ using rheology. A comparison between GδL and a conventional HCl trigger is presented. Branched copolymer-stabilised ethyl acetate o/w emulsions were used as templates in the production of both pH-responsive, surface-functionalised poly(methyl methacrylate) (PMMA) colloidal nanoparticles and non-responsive PMMA particles via an emulsion-solvent-evaporation technique. Lowering of the solution pH can trigger the reversible aggregation of these highly dispersed pH-responsive colloids into 3D structures with internal macroporosities dictated by the method of dehydration employed. The colloids can also co-encapsulate various hydrophobic molecules without any effect on particle stability and pH-responsiveness. The production of multi-responsive emulsion droplets via the encapsulation of oleophilic, magnetic Fe3O4 nanoparticles within a stable, surface-functionalised dodecane o/w emulsion was investigated. Droplet surface functionality allowed the formation of EE on lowering the pH, and encapsulated nanoparticles gave both the free-flowing and aggregated emulsions magnetic-responsiveness. The rate of aggregation and gel strength of multi-responsive EEs is compared to that of a standard pH-responsive emulsion.