Phase behavior and phase structure of 1:1 salt-free catanionic surfactant dodecyltrimethylammonium decanoate

The salt-free catanionic surfactant dodecyltrimethylammonium decanoate (DTAD) was synthesized by a novel method. Phase behavior and phase structure of DTAD with water at full concentration range were studied at 20–45 °C, using differential scanning calorimetry (DSC), freeze-fracture transmission electron microscopy (FF-TEM), polarization microscopy, and small-angle X-ray diffraction (XRD) techniques. The DTAD–water system formed a large aqueous multi-phase region, a large lamellar liquid crystal (Lα phase) region, and a hydrated crystal phase. The densely packed vesicles and the lamellar structure induced the formation of aqueous multi-phase region. With increasing temperature, the multi-phase region and the Lα phase region reduced, and the isotropic solution phase (L1 phase) appeared.