VEM observation of molecular assemblies in iridescent surfactant solutions

Aqueous solutions of alkyldimethylamine oxides (CnDAO, n = 14, 16, 18, hexadecenesuccinic acid (C16SA), and diglycerol isostearyl ether (C18DGE) were observed with the video-enhanced differential interference contrast microscope (VEM). Flat plate-like assemblies were seen in iridescent solutions of C16DAO and C18DAO, while globular vesicle-like assemblies were formed in iridescent solutions of C14DAO mixed with hexanol and decane, C16SA, and C18DGE. Similar assemblies were also observed in the dilutions of iridescent solutions which displayed no iridescence. Whereas plate-like assemblies of C16DAO disappeared above 30°C, assemblies of C18DAO changed above 50°C from plate-like to globular. The relation of the iridescence to the molecular assemblies in surfactant solutions is discussed.