Formation of α-gel (α-form hydrated crystal) by oleic acid-based gemini surfactant

In this study, we prepared an alpha-gel (alpha-type or alpha-form hydrated crystal) using an oleic acid-based gemini surfactant bearing carboxylate headgroups (anti-CC-9,9-EsH10-Na). Small- and wide-angle X-ray scattering (SWAXS) data showed that ternary mixtures of anti-CC-9,9-EsH10-Na, 1-tetradecanol (C14OH) and water formed a highly ordered alpha-gel. The SWAXS results also suggested that an increased C14OH molar content resulted in increased d-spacing in the lamellar structure of the alpha-gel. We studied the mobility of protons in the alpha-gel system through spin-spin relaxation time (T-2) measurements using H-1-nuclear magnetic resonance (NMR) spectroscopy. The C14OH molar content significantly affected the mobility of protons originating from alkyl chains. In addition, an increased C14OH molar content resulted in the morphological transformation of the alpha-gel domain from a lamellar network structure into an onion-like structure. We suggested that the morphological transformation and the excess water surrounding the alpha-gel domains are among the key factors that determine the viscosity of the alpha-gel system.