Structures of nanoparticles prepared from oil-in-water emulsions

• Nanometric particles of three mixtures of hydrophobic substances, cholesteryl esters, have been prepared by emulsification in water. These substances were dissolved in an organic solvent which was emulsified with an aqueous solution at very high shear. Droplets of very small sizes (50-100 nm) were obtained using surfactants which were combinations of lecithins and bile salts. After the emulsification was completed, the organic solvent was removed by evaporation, yielding stable suspensions of solid particles. The sizes of these particles did not follow the reduction expected from the removal of organic solvent, indicating that the particles were not dense spheres. According to cryo-transmission electron microscopy and to small angle neutron scattering (SANS) the newly prepared particles are non-aggregated. Furthermore, the results suggest that the emulsifier used in the preparation of the emulsion and the particle core composition determines the morphology of the obtained particles. a) The shape of choleateryl acetate particles stabilized by lecithin and sodium glycocholate was examined by cryo-transmission electron microscopy; and it was found that the particles were platelets with a thickness of 10-20 nm and a diameter of 100 nm. The structures of the particles were also examined by small angle neutron scattering; these results were consistent with a platelet structure. Upon storage at high concentration in water, some aggregation was observed, but the particles remained individual platelets. b) Cholesteryl acetate particles prepared with a sorbitan ester were, on the other hand, spherical according to cryo-transmission electron microscopy and SANS measurements. c) Samples prepared with lecithin as emulsifier and a lipid mixture in the core were

Nyckelord

Nanoparticles

cholesteryl acetate

o/w emulsions

cryo-transmission electron microscopy

small angle neutron scattering

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