STRUCTURES OF NANOPARTICLES PREPARED FROM OIL-IN-WATER EMULSIONS

Hydrophobic substances were dissolved in an organic solvent and emulsi fied with an aqueous solution at very high shear. Droplets of very sma ll sizes (50-100 nm) were obtained by using surfactants which were com binations of lecithins and bile salts. After emulsification, the organ ic solvent was removed by evaporation, yielding stable dispersions of solid particles. The sizes, shapes, and structures of the particles we re examined through quasi-elastic light scattering, small-angle neutro n scattering and cryotransmission electron microscopy. Cholesteryl ace tate particles stabilized by lecithin and bile salts were found to be platelets of 10-20 nm thickness and 80 nm diameter. Cholesteryl acetat e particles stabilized with POE-(20)-sorbitan monolaurate were dense s pherical globules of diameter 100 nm. Particles with a composition sim ilar to the endogenously occurring lipoprotein, LDL, were large spheri cal globules studded with small vesicles. The subsequent evolution of the cholesteryl acetate dispersion upon aging was examined. There was no transfer of cholesteryl acetate between particles nor to large crys tals. However, some aggregation of the particles was observed when the volume fraction of the particles in the aqueous dispersion exceeded 0 .05. Thus, the structure of the nanoparticles obtained through deswell ing of emulsion droplets changes according to the nature of the emulsi fiers and to the composition of the hydrophobic substances which they contain.