A gel state from densely packed multilamellar vesicles in the crystalline state

A salt-free, cationic and anionic (cat-anionic) fluoro/hydrocarbon surfactant system comprised of tetradecyldimethylaminoxide (C14DMAO) and perfluorolauric acid (PFLA) shows novel phase behavior and structure. A classic micelle phase (L1), an L1/Lα two-phase, a birefringent Lα-phase, an L1/P two-phase, a birefringent gel-phase, and another L1/P two-phase are observed in the system. Solutions of 100 mmol L−1 L1 and birefringent Lα and gel phases, at PFLA mole fractions XPFLA = 0.10, 0. 25, and 0.85, respectively, were further characterized. The gel phase is an elastic, network aqueous gel, and made from close-packed multilamellar vesicles. The atomic force microscopy (AFM) images indicated that the aqueous gel is formed from densely packed vesicles. Small-angle X-ray scattering was used to demonstrate the microstructure of the gel-phase. DSC measurements were used to determine the temperature-dependent transitions of fluorinated alkyl chains of PFLA, the results of which indicate that the fluorocarbon chains are in the crystalline state at room temperature. This is the first example of a network aqueous gel formed from closely-packed vesicles in a salt-free cat-anionic surfactant mixture.