Effect of Temperature, Oil Type, and Copolymer Concentration on the Long-Term Stability of Oil-in-Water Pickering Nanoemulsions Prepared Using Diblock Copolymer Nanoparticles

A poly(glycerol monomethacrylate) (PGMA) precursor was chain-extended via RAFT aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA). TEM studies confirmed the formation of well-defined PGMA52–PTFEMA50 spherical nanoparticles, while DLS studies indicated a z-average diameter of 26 nm. These sterically-stabilized nanoparticles were employed as emulsifiers to prepare oil-in-water Pickering nanoemulsions by (i) high-shear homogenization and (ii) high-pressure microfluidization using either n -dodecane or squalane as the droplet phase. The long-term stability of such Pickering nanoemulsions was evaluated by analytical centrifugation over a four-week period. The higher aqueous solubility of n -dodecane compared to squalane led to a significantly faster rate of Ostwald ripening. Adding squalane to n -dodecane prior to emulsification suppressed this instability mechanism, as judged by analytical centrifugation studies. The nanoparticle adsorption efficiency at the n -dodecane-water interface was assessed by gel permeation chromatography. Increasing the nanoparticle concentration from 4.0 to 10% w/w produced smaller droplets but also reduced the adsorption efficiency, as confirmed by TEM studies. Furthermore, the effect of varying the nanoparticle concentration (2.5 to 10% w/w) on the long-term stability of n -dodecane-in-water Pickering nanoemulsions was explored over a four-week period. Nanoemulsions prepared using higher nanoparticle concentrations were more unstable and exhibited a faster rate of Ostwald ripening. The nanoparticle adsorption efficiency was monitored for an aging nanoemulsion prepared using a nanoparticle concentration of 2.5% w/w. As these droplets ripened over time, the adsorption efficiency remained constant (~97%). This suggests that nanoparticles desorb from the shrinking smaller droplets and then readsorb onto growing larger droplets over time. Finally, the effect of temperature on the stability of Pickering nanoemulsions was examined. Storing these Pickering ...