Department of Chemical and Materials Engineering, Tamkang University, No.151, Yingzhuan Road, Tamsui District, New Taipei City 25137, Taiwan.
J Phys Chem B. 2013 Aug 15;117(32):9568-75. doi: 10.1021/jp4062913. Epub 2013 Aug 5.
This paper discusses the phase behavior, rheology, and structure of self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle systems at high AOT concentrations. When the amount of AOT and w(o) (the molar ratio of water to AOT) were changed, many different phases were found, a fact which is not discussed in the literature. Opaque gel-like phase (phase separation) occurred with high concentrations of AOT in organic solvents without water. When the AOT concentration and w(o) were increased to 18-72 m and 2, respectively, the samples were gel-like and translucent. Dynamic rheological results indicate that the viscoelastic transition agreed with a multirelaxation time model. Small-angle X-ray scattering (SAXS) results imply that these samples showed a hexagonally close-packed cylindrical structure in which the diameter of a cylinder was ~2.5-3.0 nm, depending on the water contents. Moreover, these AOT cylinders self-assembled into fiber bundles with a diameter of 1-10 μm, as determined using a polarized optical microscope. As w(o) was increased to 2-6 in 72 m AOT samples, similar rheological and SAXS results were obtained. However, a different type of viscoelastic transition occurred, from multirelaxation to single-relaxation, when w(o) was increased to 7-11. The samples were in the transparent gel-like phase, and the structures determined by SAXS were a combination of hexagonally packed cylindrical and lamellar structure. The close-packed cylindrical structures had larger radii and shorter lengths with increasing w(o). Furthermore, when w(o) was increased to 12, the gel-like phase disappeared and a highly viscous solution was observed. This is because all the cylindrical structures collapsed and transformed into lamellar structures when the amount of water was further increased.
本文讨论了在高 AOT 浓度下，自组装的双（2-乙基己基）磺基琥珀酸钠（AOT）反胶束体系的相行为、流变学和结构。当 AOT 的量和 w(o)（水与 AOT 的摩尔比）发生变化时，发现了许多不同的相，这在文献中并没有讨论过。在没有水的有机溶剂中，当 AOT 的浓度较高时，会出现不透明的凝胶状相（相分离）。当 AOT 浓度和 w(o)分别增加到 18-72 m 和 2 时，样品呈凝胶状和半透明状。动态流变学结果表明，粘弹性转变符合多松弛时间模型。小角 X 射线散射（SAXS）结果表明，这些样品呈现出六边形紧密堆积的圆柱状结构，其中圆柱的直径约为 2.5-3.0nm，取决于含水量。此外，这些 AOT 圆柱在偏振光显微镜下自组装成直径为 1-10μm 的纤维束。当在 72 m AOT 样品中 w(o)增加到 2-6 时，得到了类似的流变学和 SAXS 结果。然而，当 w(o)增加到 7-11 时，发生了不同类型的粘弹性转变，从多松弛转变为单松弛。样品处于透明凝胶状相，由 SAXS 确定的结构是六方堆积圆柱和层状结构的组合。随着 w(o)的增加，紧密堆积的圆柱结构的半径增大，长度变短。此外，当 w(o)增加到 12 时，凝胶相消失，观察到高度粘稠的溶液。这是因为当水量进一步增加时，所有的圆柱结构都坍塌并转化为层状结构。
