Phase diagrams of water–alkyltrimethylammonium bromide systems

Phase diagrams of water–alkyltrimethylammonium bromide (CnTAB, n = 10, 12, 14 and 16) systems were measured as a function of the temperature and the total surfactant concentration. All CnTABs form an isotropic solution (L1), a hexagonal liquid crystalline phase (H1), a cubic phase (V1) and a lamellar phase (Lα) with increasing surfactant concentration. The size of the alkyl chain length of the surfactant influences the extension of the liquid crystalline phases; the shorter the alkyl chain the smaller the extension of the liquid crystalline region. In the case of the pseudobinary system H2O–C10TAB/C16TAB a shrinking of the H1 phase was observed. The structure of the H1 phases was investigated by means of small angle X-ray scattering (SAXS) and polarizing microscopy.