We study the phase behavior, rheology and structure of self-assembled gels prepared by adding minute amounts of water to organic solutions of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) at high concentrations. Macroscopic phase separation (opacity) occurred at high AOT concentrations in a range of organic solvents, such as hexane, heptane, and isooctane. Here, we found that when trace amounts of water were added to these opaque, heterogeneous solutions, AOT reverse micelles formed, and self-assembled, homogeneous gels were obtained. Gels prepared from AOT in hexane, by adding different amounts of water, were chosen in this study. The rheological measurements demonstrated that the samples exhibited the gel-like behaviors. The tendency of G′ and G″ implies that the transition had a disperse spectrum of relaxation times. Small-angle X-ray scattering (SAXS) results attested that the gels showed a hexagonally closed-packed cylindrical structure, and that the structure was quite stable up to at least 75 ̊C. The radius of a micellar cylinder was around 1.35–1.40 nm, depending on the addition of different water contents by SAXS. However, the radius of a cylinder did not change significantly in solvents (heptane and isooctane) other than hexane. The AOT cylinders can self-assemble into fiber bundles of 1–10 μm in diameter with rough alignment, as observed by a polarized optical microscope (POM).
Colloids and Surfaces A: Physicochemical and Engineering Aspects 433, pp.139–144