Phase behavior and aggregate structure in aqueous mixtures of sodium cholate and glycerol monooleate

The phase behavior of the glycerol monooleate (GMO)-sodium cholate-water (o r 0.9 wt% NaCl) system has been examined in the solvent-rich part, using sm all-angle X-ray scattering and conventional methods. Addition of cholate up to 7% of the total amphiphile swells the cubic phase of the binary GMO-wat er system so that it takes up almost 70% of water in the salt-free case and 55% in salt, With more bile salt the lamellar phase also appears highly sw ollen (up to 85% in water, 75% in brine). In the salt solution a small isot ropic L-3-phase region replaces the lamellar phase at a solvent content of about 79%. The lamellar phase can accept only about 0.2 cholate molecule pe r GMO, in both water and brine, and a phase with globular micelles (L-1) fo llows and dominates the diagram. No threadlike micelles appear in this syst em. Investigation of the particle structures with cryo-transmission electro n microscopy (TEM) in dilute systems (99% solvent) show globular micelles a nd coexisting vesicles and globular micelles, In the presence of salt, dilu tion of the L-3 phase results in dispersed globular particles with an irreg ular internal morphology that suggests they are a dispersed L-3 phase. Thes e particles coexist with faceted particles having an inner structure giving a hexagonal pattern in projection, suggested to derive from the cubic phas e. The cubic phase in the salt-free systems did not give dispersions stable enough for cryo-TEM examination. (C) 1999 Academic Press.