Emulsions stabilized with organic solid particles

Biodegradable and biocompatible o/w emulsions were prepared using triglyceride oil and solid organic particles made of block copolymer nanoparticles as stabilizers (Pickering emulsions). In order to reach high concentration of internal phase, rather concentrated dispersions of nanoparticles were required. Nanoparticles of poly(caprolactone)-block-poly(ethylene oxide) (PCL-b-PEO) diblock copolymer were obtained using the “nanoprecipitation” process relying of the spontaneous emulsification upon solvent shifting. The classical “nanoprecipitation” process was improved so as to afford more concentrated suspensions of nanoparticles, and the nanoparticles were characterized by means of dynamic light scattering and 1H NMR spectroscopy. The process allowed the preparation of aqueous dispersions of PCL-b-PEO nanoparticles with 35–50 nm diameter at concentrations over 5 wt.%. In D2O, the PCL blocks formed a central hydrophobic core of reduced mobility, while the PEO blocks formed a hydrophilic corona layer swollen by water. O/w emulsions of medium chain triglycerides were successfully prepared using the suspensions of PCL-b-PEO nanoparticles as stabilizers. Typical droplet sizes were between 2 μm and 15 μm. The emulsions showed great stability upon storage and their particle size distributions did not show excess nanoparticles present in the aqueous phase as submicron nanoparticles, even when large amounts of nanoparticles with respect to oil were used. The mean droplet diameter of emulsions was controlled by the mass ratio M(oil)/M(nanoparticles). SANS and TEM experiments performed on PCL-b-PEO nanoparticles and micelle-stabilized emulsions disclosed a rearrangement of the nanoparticles at the oil/water interface due to the liquid state of the micelle core of PCL.