(450c) Solvent Absorbent Amphiphilic Microgels for Pickering Emulsions

Pickering emulsions are critical to systems where encapsulation of an oil or water phase in an immiscible medium is required. These coated emulsions can harbor oils in water or even water in oils. While hard particles are traditionally used, microgel particles have also been used as emulsion stabilizers. These polymer colloids differ from rigid particles in many ways. When compared to microgels, colloidal particles are lyophobic, meaning they need surface modification to be preferably “wet” by a solvent. Microgels can be made to be lyophilic, having an attraction to the solvent that swells them. Microgels are cross-linked polymer networks that absorb and desorb solvents where the type of solvent used to swell a microgel can be tailored during particle synthesis.

Using a Polydimethylsiloxane microfluidic device, via soft lithography, the flow streams of two separate polymer solutions were brought into contact to form Janus droplets. The individual droplets were then exposed to UV light to induce cross-linking via photo-polymerization to form monodispersed microgel particles with sectioned hydrophilic and hydrophobic sides. 45 wt% Polyethylene Glycol diacrylate (PEGDA), 5 wt% ethoxilated trimethylopropane triacrylate (ETPTA), 1 wt% 2-hydroxy-2-methyl-propiophenone (HMP), and 49 wt% water were mixed together to form the hydrophilic portion while 99 wt% Polypropylene Glycol diacrylate (PPGDA)) and 1 wt% 2-hydroxy-2-methyl-propiophenone are added together to form the hydrophobic side. In crosslinking these two systems together, we form single particles that have one side capable of absorbing water and another with the ability to absorb and desorb organic solvents. These particles were used to make stable water in oil and oil in water Pickering emulsions.

PEG functionalized CdSe/ZnS core-shell type quantum dots in water and CdSeS/ZnS alloyed quantum dots in toluene were used to observe the absorption abilities of the hydrophilic and hydrophobic microgel sides respectively with a confocal microscope. While oriented at the water/oil interfaces, the respective microgel sides swell and capture the dispersed nanocrystals. These amphiphilic microgels pose as an interesting tool in stabilizing emulsion droplets for cosmetic, pharmacy, and petroleum industries.