DISPERSION BEHAVIOR OF OLEIC-ACID IN AQUEOUS-MEDIA - FROM MICELLES TOEMULSIONS

Dispersion behavior of aqueous solutions containing oleic acid (RH), s odium oleate (R-Na+), and NaCl was investigated by turbidity and dynam ic light-scattering measurements. Changes of the size of scattering pa rticles in solution composed of 1 mM oleic acid and 100 mM NaCl were t raced as a function of the degree of ionization alpha, in terms of rad ius of the equivalent hydrodynamic sphere. Large associated micelles w ith a radius of 30 nm appeared by a slight decline of alpha and existe d at alpha higher than 0.75. They were responsible for the three-phase equilibrium (solution, micelle and aggregated micelle, and acid-soap, (R-Na+)(3)RH) characterized by a constant pH of 9.75. The appearance of a new phase, (R-Na+)(3)RH, contributed to increase both the turbidi ty and averaged scattering particle size. As the breakdown of the thre e-phase equilibrium, radius of scattering particles increased signific antly. Finally, oleic acid oil droplets were separated from aqueous ph ase at low alpha. When the system was buffered by tris (hydroxymethyl) aminomethane (Tris), scattering particles with a weight-averaged hydro dynamic radius of 75 nm existed in a wide range of alpha from 0.85 to 0.65. In Tris buffered solution, turbidity formation was induced by th e increase in the number of aggregated particles.