AUTO-OXIDATION OF LINOLEIC ACID 287 PREPARATION OF O/W EMULSIONS The compositions are reported in Table II. Emulsions of low viscosity were prepared. Hexadecanol was dissolved in IPM, LH, and Tween 20 then the mixture was added to a dispersion of Carbomer 1342 in water. The continuous phase of the emulsion was brought to ca. pH 5 by adding glucosamine in order to have a similar pH in all the systems. This pH ensures partial dissociation of the carboxylic group of carbomer 1342. The emulsions were also prepared in the presence of AIBN and of ot-T. In order to have fluid emulsions, the emulsifier concentration was maintained lower than that in the microemulsions and in the miceliar systems. Fluidity is necessary in order to obtain reliable 02 measurements. PREPARATION OF O/W MICROEMULSIONS The compositions of the different microemulsions are reported in Tables III and IV. The surfactant was dissolved at room temperature in the oil then either 1-butanol or 2-ethyl-1,3-hexanediol was added. The whole mixture was then added under shaking to the continuous phase, consisting of water or of a mixture of 1,2-propanediol and water clear systems were obtained. The microemulsions in the presence of LH, AIBN, and ot-T were prepared as described above, after first dissolving the radical initiator and the antioxidant in the disperse phase. About the same concentrations of emulsifier as those used in the miceliar solu- tions were employed. CHARACTERIZATION OF THE MICROEMULSIONS The microemulsions are transparent dispersions of water, oil, surfactant, and cosurfac- tant. The disperse phase has a droplet structure, even if bicontinuous structures are also observed. The quasi-elastic light-scattering technique (QELS) was used to determine the average diameters of the microemulsion droplets. Stabilities of the systems were also checked by conductivity and viscosity at 37øC no appreciable changes were observed after 30 days. The data are reported in Table V. Table II Emulsion Compositions and Rate of Oxidation of Linoleic Acid in the Presence, Rp, and in the Absence, Rinh, of o•-T ISM Tween 20 Water Hexadecanol Emulsion (% w/w) (% w/w) (% w/w) (% w/w) Carbomer ot-T AIBN Ri• ) Rin h 1342 LH (M x (M x x 9 ) 10 9 (% w/w) (% w/w) 10 4) 10 3) (M/s) (M/s) 1 2.00 1.11 93.95 0.25 2 2.00 1.11 93.95 0.25 3 2.00 1.11 93.95 0.25 4 2.00 1.11 93.95 0.25 0.12 2.57 -- -- 22.58 -- 0.12 2.57 -- 9.46 75.39 -- 0.12 2.57 1.56 -- -- 11.10 0.12 2.57 1.56 9.46 -- 38.30

288 JOURNAL OF•THE SOCIETY OF COSMETIC CHEMISTS Table III Microemulsion Compositions With Water as External Phase IPM Tween 20 ButOH HexOH LH ot-T AIBN Water Microemulsion (% w/w) (% w/w) (% w/w) (% w/w) (% w/w) (M x 104) (M x 103) (% w/w) 1 5.01 24.06 11.94 -- -- -- 58.99 2 4.98 23.90 11.86 -- 0.66 -- 58.60 3 4.98 23.90 11.86 -- 0.66 -- 2.46 58.60 4 4.95 23.74 11.79 -- 1.31 -- 58.21 5 4.95 23.74 11.79 -- 1.31 -- 4.80 58.21 6 4.91 23.59 11.71 -- 1.95 -- 57.83 7 4.91 23.59 11.71 -- 1.95 -- 6.87 57.83 8 4.88 23.43 11.64 -- 2.59 -- 57.46 9 4.88 23.43 11.64 -- 2.59 -- 9.47 57.46 10 4.88 23.43 11.64 -- 2.59 1.56 9.47 57.46 11 4.88 23.43 11.64 -- 2.59 6.11 9.47 57.46 12 4.92 23.63 -- 13.51 -- -- 57.94 13 4.89 23.47 -- 13.43 0.65 -- -- 57.56 14 4.89 23.47 -- 13.43 0.65 -- 2.46 57.56 15 4.86 23.32 13.34 1.29 -- 57.19 16 4.86 23.32 13.34 1.29 -- 4.61 57.19 17 4.83 23.17 -- 13.26 1.92 -- 56.82 18 4.83 23.17 -- 13.26 1.92 -- 5.37 56.82 19 4.80 23.03 -- 13.17 2.55 -- -- 56.45 20 4.80 23.03 -- 13.17 2.55 -- 9.47 56.45 21 4.80 23.03 -- 13.17 2.55 1.56 9.47 56.45 22 4.80 23.03 -- 13.17 2.55 6.11 9.47 56.45 Density range of microemulsions: with ButOH = 0.985-0.990 with HexOH = 1.001-1.004. CHARACTERIZATION OF THE MICELLAR SOLUTIONS Stabilities of the systems were checked by conductivity and viscosity. The pH, the conductivity, and the viscosity of the micellar solution 2 were 5.0, 0. 123 mS, and 10.64 cSt, respectively no appreciable changes were observed after 30 days. CHARACTERIZATION OF EMULSIONS Optical microscopy was used to determine mean diameters of the droplets of the emul- sions. The mean diameter of the droplets was measured after the stability test (performed maintaining the emulsion at 37 ø for three hours). The mean diameters of the droplets of the emulsions diluted with water (in a ratio 1:500, 1:1000) were also determined by photocorrelation laser spectroscopy. The mean diameter with laser spectroscopy was 337.7 nm (polydispersity 0.295). The mean diameter with microscopy was 900 nm. The viscosity of emulsion 1 was 119.37 cSt, and the pH was 5.0. MEASUREMENTS OF OXYGEN UPTAKE The rate of oxidation of finoleic acid, determined by following the decrease of oxygen concentration in solution, was monitored by the Biological Oxygen Monitor. The