Phase Behavior and Light Scattering of the System Dodecyldimethylaminoxide, n‐Hexanol and Water in the Very Dilute Region

Solutions of Dodecyldimethylaminoxide (DDMAO), n‐hexanol and water show a phase behavior which is found to be typical for many surfactant‐alcohol‐water systems with lamellar phases. Three types of lamellar phases and three types of isotropic low viscous clear phases which exhibit extreme flow birefringence (L3‐phases) are found at room temperature. Both a hexanol‐rich (Lαh) and a hexanol‐poor lamellar phase (Lαl) can be diluted to iridescent solutions with bright colors. The iridescent Lαh phase is of low viscosity and forms quickly, the higher viscous Lαl phase needs 600 hours until the iridescence can be observed. — UV‐Vis and classical light scattering measurements show that the interlamellar structures or spacings of the Lαl phase are strongly and those of the Lαh phase are weakly fluctuating. The Lαh phase is much more sensitive to added electrolyte than the Lαl phase. The Lαl phase seems to be the type of iridescent phases which can be found with some ionic surfactant‐water systems. — An intermediate lamellar phase exists between the Lαh and the Lαl phase with a second order or kinetically controlled phase transition. At the lower concentration limit (DDMAO concentration around 50 mmol/l) this intermediate phase needs several months for the formation. — The Lαh phase is accompanied at some higher hexanol concentration by a L3 phase. This phase transforms quickly to an iridescent phase immediately after shear stress. Depending on concentration and temperature this iridescent phase remains stable for a few minutes to several hours. The second isotropic phase with extreme flow birefringence exists below the Lαl phase. Dilution of the intermediate lamellar phase leads to an intermediate phase of type L3 which is not in a thermodynamic equilibrium state. — The Lαl phase and the intermediate lamellar phase give slow torsion waves whose propagation can be observed between crossed polarizers. The rheologic behavior which leads to these shear waves is discussed.