Effect of Surfactants on Iridescence Developed by Swollen Lamellar Phase of C12-Alkenylsuccinic Acid

Abstract

The iridescence phenomenon of C 12 -alkenylsuccinic acid (ASA) is a result of the coherent reflection of light from periodically ordered alternating lamellar surfactant stacks and solvent molecules. Here we report the effect of cationic, anionic, and nonionic surfactants on the iridescence of ASA. It was observed that ionic surfactants resulted in destabilization of the iridescence of ASA, while the addition of nonionic surfactant stabilized the system. The nature of the interactions of these surfactants on ASA was investigated using reflectance spectroscopy, differential scanning calorimetry, optical microscopy, and small angle X-ray scattering (SAXS). The bilayer thickness was determined using reflectance spectra, SAXS, and theoretical calculations. It was observed that the nonionic surfactant does not alter the lamellar spacing of ASA, while ionic surfactant was seen to lower it by creating water-filled defects. The diffraction patterns also exhibit an additional broad peak which indicates formation of uncorrelated bilayers. This study thus provides understanding of such swollen lamellar systems.