Phase and aggregation behaviour of double-chain cationic surfactants from the class of N-alkyl-N-alkyl '-N, N-dimethylammonium bromide surfactants

We present the phase diagrams and the properties of newly synthesised doubl e-chain cationic N-alkyk-N-alkyl'-N,N-dimethyl-ammonium bromide surfactants [C(x)C(y)DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the sy stems studied form liquid-crystalline lamellar phases but with different mo rphologies: unilamellar vesicles at low surfactant concentrations, multilam ellar vesicles and tubular aggregates for surfactant concentrations between 2 and 10 wt% and at even higher concentrations planar bilayers of surfacta nt molecules in the classical L-alpha phase. The phase diagrams were determ ined with macroscopic and microscopic methods (polarisation microscopy, fre eze-fracture transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination and small-angle neutron scatte ring measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and viscosity measurements for phase characterisation were ca rried out.