Reversible addition-fragmentation chain transfer (RAFT) solution polymerization is used to prepare well-defined poly(glycerol monomethacrylate) (PGMA) bearing either carboxylic acid, tertiary amine or neutral end-groups. These PGMA precursors were then chain-extended via RAFT aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) to form PGMA48-PTFEMA50 spherical nanoparticles of approximately 20 nm, as confirmed by TEM studies. Zeta potential studies confirmed that the amine-functional nanoparticles became cationic (~ +25 mV) at low pH owing to end-group protonation. In contrast, carboxylic acid-functional nanoparticles became anionic (~ -25 mV) at pH 10 owing to end-group ionization. Finally, the nanoparticles bearing neutral end-groups exhibited almost zero zeta potential (0 to -10 mV) over a range of solution pH. High shear homogenization of such nanoparticles in the presence of n-dodecane led to the formation of oil-in-water Pickering macroemulsions of 30 - 50 µm diameter. High-pressure microfluidization was then used to prepare the corresponding three Pickering nanoemulsions. Each Pickering nanoemulsion was characterized by TEM studies and analytical centrifugation. The nanoparticle adsorption efficiency at the oil-water interface was assessed by gel permeation chromatography (GPC) for all three nanoparticles at both pH 3 and 7 using a UV detector (set to λ = 305 nm, which corresponds to the absorption maximum of the RAFT end-groups). Nanoparticles with charged end-groups exhibited relatively low adsorption efficiency, whereas neutral nanoparticles had efficiencies of around 90%. Analytical centrifugation was used to evaluate the colloidal stability of the aged Pickering nanoemulsions. Pickering nanoemulsions stabilized with nanoparticles bearing charged end-groups proved to be significantly less stable than those prepared using neutral end-groups.

How does end-group charge on the steric stabilizer block affect the formation and stability of Pickering nanoemulsions prepared using diblock copolymer nanoparticles?

2019 Fall National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.