Development of Novel Pickering Emulsifiers using Polymer Grafted Nanoparticles

Pickering emulsions utilize colloidal particles as emulsifiers at particle concentrations typically on the order of one percent.1 In the work presented, silica nanoparticulate emulsifiers with polymer brushes grafted from their surfaces by atom transfer radical polymerization (ATRP) were created. The polymer modification to Pickering emulsifiers results in a reduction of interfacial tension which further enhances emulsifying efficiency. Similarly, polymer star structures with a dense polymeric core and emanating polymer arms were synthesized via ATRP and shown to be effective emulsifiers. With a dense core and emanating arms, they share the basic structure of a core nanoparticle with a polymer brush shell. This work examined the role of polymer brush composition, degree of polymerization, grafting density and architecture in emulsification.;The polymer grafted nanoparticles developed in this study include SiO 2 - PDMAEMA (poly(2-dimethylamino)ethyl methacrylate)), SiO2 - M(EO)2MA (di(ethylene glycol) methyl ether methacrylate) - POEO 475MA (oligo(ethylene oxide) methyl ether methacrylate) and SiO 2 - PBA (poly(butyl acrylate) - POEO475MA. The most efficient emulsifier was SiO2 - M(EO)2MA-POEO 475MA, which stabilized xylene and cyclohexane in water emulsions with particle concentrations of only 0.0053 and 0.008 wt% respectively. These concentrations are an order of magnitude less than the most efficient particulate emulsifier system previously reported in the literature (0.04 wt% for poly(styrene sulfonate)-grafted silica nanoparticles).2 Star polymers of PEO (poly(ethylene oxide), PAA (poly(acrylic acid) and PDMAEMA were also highly efficient, stabilizing emulsions with only 0.01 wt% particles. Synergy was observed with mixtures of the SiO2 - PDMAEMA particles and star PEO, resulting in enhanced efficiency in comparison to either emulsifier individually.;Polymer grafting from nanoparticles is of interest as a route to pH and thermally tunable emulsification, for example when the polymer has pH or temperature dependent solution characteristics. Thermally responsive emulsions were created with SiO2 - PDMAEMA particles that rapidly broke by increasing the temperature above the critical flocculation temperature of the particles in water. Emulsions stabilized with PBA-PAA miktoarms formed pH responsive emulsions.;In addition to emulsification properties of these nanoparticle-grafted polymer brush structures, their interfacial activity at fluid interfaces was measured, and in one case, PEO stars, their adsorption to the solid/liquid interface was measured and compared to the equivalent homopolymer.