Nanoemulsions and Nanocapsules with Oleic Acid

Nanoemulsions are promising disperse systems that can be used as carriers of hydrophobic drugs and biologically active compounds. In this work, nanoemulsions, which contain oleic acid as a dispersed phase and are stabilized with mixtures of nonionic surfactants, Tween 80/Span 80 and Tween 60/Span 60, have been studied. Nanoemulsions stabilized with Tween 80 and Span 80 are unstable. Dispersed phase droplets of such systems undergo intense flocculation and coalescence. Nanoemulsions stabilized with Tween 60 and Span 60 have appeared to be much more stable. The average particle diameter of the dispersed phase remains almost unchanged for a long time at 25°C, as well as in two cycles of heating to 60°C and subsequent cooling to 5°C. Microcalorimetry has been employed to determine the temperatures of phase transitions in such nanoemulsions. The obtained thermograms have two peaks due to melting of oleic acid and a mixed adsorption layer consisting of Tween 60 and Span 60 molecules. Since a solid shell is formed on the surface of oleic acid droplets, such systems can be considered to be nanocapsules.