Phase behaviour and physical properties of the cationic quaternary system tetradecyldimethylamine oxide hydrochloric acid 1-hexanol water

The phase behaviour and properties of the tetradecyldimethylamine oxide/HCl /hexanol/water quaternary surfactant system have been studied by means of e lectric conductivity, rheology, freeze-fracture transmission electron micro scopy (FF-TEM) and small-angle neutron scattering (SANS). In this system th e originally zwitterionic surfactant can become increasingly charged by pro tonation through the addition of HCl, i.e. the degree of charging can be ch anged continuously. An interesting, isotropic phase (LT phase) of low visco sity was observed for intermediate degrees of charging. From viscosity and conductivity measurements this phase can clearly be distinguished from the conventional L-1 phase that is composed of micelles. Investigation of the s tructures present by means of FF-TEM and SANS wshowed that the L-1* phase i s made up of unilamellar vesicles of extremely small diameter of 8-10 nm. E vidently such highly curved structures are stabilized by the electrostatic conditions in this system.