Bespoke diblock copolymer nanoparticles enable production of relatively stable oil-in-water Pickering nanoemulsions

Sterically-stabilized diblock copolymer nanoparticles with an intensity-average diameter of 25 nm are prepared in the form of a concentrated aqueous dispersion using polymerization-induced self-assembly (PISA). Addition of n-dodecane followed by high-shear homogenization produces n-dodecane-in-water Pickering macroemulsions of 22-46 µm diameter. If the nanoparticles are present in sufficient excess, subsequent processing using a high-pressure microfluidizer leads to formation of Pickering nanoemulsions with a mean droplet diameter below 200 nm. The size of these Pickering nanoemulsions can be tuned by systematically varying the nanoparticle concentration, applied pressure, the number of passes and the oil volume fraction. High internal phase emulsions can also be achieved by increasing the n-dodecane volume fraction up to 0.80. TEM studies of (dried) n-dodecane droplets confirm the presence of intact nanoparticles and suggest a relatively high surface coverage, which is consistent with model packing calculations based on radius ratios. Such Pickering nanoemulsions proved to be remarkably stable with respect to Ostwald ripening, with no significant change in the mean DLS droplet diameter after storage for approximately four months at 20 °C.