Small-angle X-ray scattering as an effective tool to understand the structure and rigidity of the reverse micelles with the variation of surfactant

Abstract

This study is aimed to utilize the small-angle X-ray scattering technique for getting new insights on the effect of the structure of surfactants on the shape, size, thickness of the diffusion layer, and rigidity of the reverse micelles, formed within a water-in-oil microemulsion. For this study, two important features of the structure of the surfactant i.e. hydrophobic alkyl chain length and the nature of the hydrophilic head group (cationic, anionic, and non-ionic) are taken into consideration. The primary information regarding the shape, diffusion length, and internal structure of reverse micelles was evaluated using the model-free approach. It was found that the reverse micelles formed in the case of cationic and anionic surfactants were spherical whereas cylindrical-shaped reverse micelles were formed with non-ionic surfactants. After critically analyzing the inferences from the model-free approach, an appropriate model for fitting the SAXS data was selected. For cationic and anionic surfactant-based microemulsions, the spherical shell model was chosen while the cylindrical shell model was used for microemulsions formed using non-ionic surfactants. We believe that this study will give a systematic approach to analyze the SAXS data and further add to our understanding of the relation between the surfactant and the structure of the reverse micelles.