Solution properties and PGSE-NMR self-diffusion study of C _18:1E₁₀/oil/water system

The microemulsion systems of polyoxyethylene-10-oleyl ether/oil/water have been studied. The medium chain triglycerides (MCT) and retinyl palmitate mixture (1:1, w/w) was solubilized up to 9% w/w at the surfactant concentration of 25% w/w. The lowest phase inversion temperature (PIT) of the microemulsion solutions was about 57°C and showed no phase separation for 6 months at room temperature. The critical micelle concentration (CMC) of polyoxyethylene-10-oleyl ether (C_18:1E₁₀) was 1.20×10^-5 M at 27°C. The phase behavior and pulsed field gradient NMR data clearly indicate that these microemulsions are discrete oil-in-water (O/W) microemulsions. The self-diffusion coefficient of free retinyl palmitate, MCT and MCT/retinyl palmitate mixture (1:1, w/w) were 1.61×10^-10, 2.60×10^-10 and 2.59×10 ^-10 m² s^-1, respectively. The D of free C _18:1E₁₀ was 4.96×10^-11 m² s^-1. The relative self-diffusion coefficients of water and oil differed by more than 1 order of magnitude. The hydrodynamic radius (R _H) of this oil swollen micelle was calculated as 14 nm at 1% w/w oil concentration (23% w/w C_18:1E₁₀, 0.5% w/w MCT, 0.5% w/w retinyl palmitate, 76% w/w water) and increased to 34 nm at 7% w/w oil concentration (23% w/w C_18:1E₁₀, 3.5% w/w MCT, 3.5% w/w retinyl palmitate, 70% w/w water).