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Lyotropic Liquid Crystalline Phases from Symmetric Double-Tailed Undecyl-, Tridecyl-, and Pentadecylbenzenesulphonates

The phase diagrams of the binary systems of alkylbenzenesulphonates/water (C11- , C13- , and C15 - surfactants with symmetric hydrocarbon double chains), were determined using crossed polarizers, polarization microscopy and 2H NMR-spectroscopy. The isotropic and lamellar phases were found. The appearance of two isotropic phases was promoted either by increasing the temperature for C11- , and C13 - surfactants, or by the addition of n-octanol. Two isotropic phases were formed at room temperatures by C15 - surfactant. The samples consisting of two isotropic phases were separated into two phases by shear, one of them isotropic and the other liquid crystalline one. The isotropic solution separates into two isotropic phases, and the liquid crystalline within one of them. The formation of liquid crystalline phase within one of the isotropic phases was also promoted by cooling of the solution from higher temperatures. Therefore, it is obvious that one of the isotropic phases is pseudo-isotropic, although optically isotropic, and, according to the spread NMR maximum from 2 to 13 Hz, it could be assumed to be a lamellar dispersion like vesicle phase in solution. The NMR spectra were kinetically controlled by following the relaxation rate of the surface water/free water exchange.

Lyotropic Liquid Crystalline Phases; Symmetric Double-Tailed; Benzenesulphonates

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