标题：Synergism and formation of vesicle gels in salt-free catanionic hydrocarbon/fluorocarbon surfactant mixtures
作者：Yang, Mei; Hao, Jingcheng; Li, Hongguang
作者机构：[Yang, Mei; Hao, Jingcheng; Li, Hongguang] Chinese Acad Sci, Lanzhou Inst Chem Phys, State Key Lab Solid Lubricat, Lanzhou 730000, Peoples R China.; 更多
通讯作者地址：[Li, HG]Chinese Acad Sci, Lanzhou Inst Chem Phys, State Key Lab Solid Lubricat, Lanzhou 730000, Peoples R China.
摘要：The surface and bulk properties of salt-free catanionic surfactant mixtures of a zwitterionic surfactant (tetradecyldimethylaminoxide, C(14)DMAO), and two partially fluorinated carboxylic acids (C6F13C2H4OC2H4COOH, TFOPA and C8F17C2H4OC2H4COOH, HFDPA) in aqueous solutions were studied. Surface tension measurements showed that strong synergism existed when C(14)DMAO was mixed with TFOPA or HFDPA, which induces a lower critical micellar concentration (cmc) and a lower surface tension at cmc (gamma(cmc)) compared to the individual surfactants. The phase behavior of both C(14)DMAO/TFOPA and C(14)DMAO/HFDPA systems in bulk aqueous solution is rich. When the molar ratio of TFOPA (or HFDPA) to C(14)DMAO was increased, an isotropic L-1 phase, an L-1/L-alpha two-phase region, a single L-alpha phase, and an L-1/precipitate two-phase region, were successively observed. At a C(14)DMAO concentration of 300 mmol L-1, the formation of gels that contain densely packed vesicles occurred. Rheological measurements showed that the viscoelasticity of the vesicle gels depends on the mixing molar ratio of the anionic surfactant to C(14)DMAO and total surfactant concentration, but is almost independent of temperature. IR spectra indicate that the hydrocarbon chains adopt a highly ordered all-trans conformation while the fluorinated chains adopt a disordered gauche conformation. Differential scanning calorimetry (DSC) measurements showed that the alkyl chains are mainly in a liquid crystalline state at room temperature.