| The phase behavior and microstructure of a biodegradable nonionic class of surfactant, alkyl monoglucosides and its mixtures, has been determined and placed into perspective with the generally known patterns known for other aqueous nonionic surfactant solutions. The binary phase behavior of long chain alkyl monoglucosides in water exhibits the characteristic cloud curve (miscibility gap) seen for many nonionics. In addition, a lower critical point cannot be observed because of the presence of a Krafft boundary. The microstructure of the surfactant-rich phase is identified as a saturated network in equilibrium with either a monomer or micellar surfactant solution. This network consists of a dense collection of junctions connected by cylindrical micelle segments.; Alkyl monoglucosides in mixture with other classes of surfactants behave nearly ideal and show only weak interactions with the different surfactant species. In contrast, strong synergistic effects are observed in the ternary phase behavior containing alkyl monoglucosides. The addition of small amounts of ionic surfactant is able to close the miscibility gap of CmG n in an extremely efficient manner, while the efficiency of nonionic additives is significantly lower. The addition of ionic surfactants increases the energy to form a junction due to electrostatic repulsion between micellar segments. On the other hand, the addition of ethoxylated alcohols, to a C mbetaG1 decreases the energetic to form micellar end caps. Both approaches are able to break up the network and overcome the miscibility gap.; Three distinct regions in the dilute isotropic region can be identified and related to the macroscopic properties observed. The zero-shear viscosity remains comparable to that of water in the region of micellization and linear micellar growth, while the viscosity increases as the micelles entangle. Finally, the formation of a dense network decreases the zero-shear viscosity by introducing stress release points. Furthermore, a lamellar liquid crystal phase, unique for C12betaG1 and ionic surfactant, forms due to electrostatic stabilization and can be swollen to reach bilayer spacings up to 100 nm. The appearance of the lamellar liquid phase is accompanied by a complex phase succession, which originates from the collision of the liquid crystal phase with the miscibility gap. |
