Reverse micelle microstructural transformations induced by oil and water

Abstract

Effects of alkyl chain length of oil and water on the shape, size, and internal structure of glycerol monooleate (GMO) reverse micelle have been investigated using small-angle X-ray scattering (SAXS) and rheometry techniques. The generalized indirect Fourier transformation (GIFT) method has been employed to analyze the SAXS data, also supported by the direct modeling. It has been found that under ambient conditions the GMO spontaneously self-structure into an ellipsoidal prolate type micelle with a maximum size of ca. 5.7 nm in n-hexane and the size increases in parallel to the chain length of oil reaching a size of ca. 10.7 nm in n-hexadecane. However, the micellar core radius remains essentially the same, i.e., the growth is one dimensional. The increasing tendency of zero-shear viscosity, η₀, with the chain length of oil further confirmed the micellar growth. The relative viscosity, η_r, of the reverse micelles was higher and exhibited a steeper solvent (chain length) dependence behavior than those predicted for a dispersion of spherical particles based on the Krieger–Dougherty relation sustaining the SAXS results. The micelles swell with water causing a significant micellar growth; the maximum size and core radius of 0.3% water incorporated reverse micelles were found to be respectively 53%, and 28% larger than the empty micelles.