Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
J Colloid Interface Sci. 2011 May 15;357(2):400-6. doi: 10.1016/j.jcis.2011.02.024. Epub 2011 Feb 15.
This study reports the unique aqueous lyotropic liquid crystal behavior of an anionic hybrid surfactant, 8F-B2ES, which has 2-[2-(butyloxy)ethyloxy]ethyl and 1H,1H,2H,2H-perfluorodecyl tails. An 8F-B2ES-analog hybrid surfactant with no oxyethylene units (8F-DeS) and a symmetric fluorinated double-tail surfactant with two 2-(1H,1H,2H,2H-perfluorohexyloxy)ethyl tails (4FEOS) were used as control surfactants in examining the effects of the oxyethylene units and of the hybrid structure on the liquid crystal behavior. Polarized microscopic observations showed the formation of a lamellar liquid crystal phase for each surfactant/water mixture at surfactant concentrations higher than 10 wt.%. In the case of the 30 wt.% 8F-B2ES/water mixture, two types of spherical aggregates were observed at temperatures higher than 40 °C: one was a typical lamella liquid crystal with a maltese cross-texture, and the other was optically isotropic. Interestingly, when the 8F-B2ES lamellar phase was cooled to below 40 °C, the lamellar aggregates were distorted and the isotropic droplets became anisotropic. As this unique liquid crystal behavior was not observed for aqueous mixtures of the control surfactants, the oxyethylene units in the hybridized hydrocarbon tail play an important role in the behavior. This study also examined the effect of the oxyethylene units on microenvironmental polarity in the hybrid surfactant bilayer via fluorescence spectral measurements of pyrene solubilized in each lamellar phase. The polarity of the 8F-B2ES bilayer at 70 °C was found to be that of a hydrocarbon surfactant lamellar phase, and increased gradually with decreasing temperature. The polarity became the same as that of hydrophilic spherical micelles below 40 °C, despite the presence of the lamellar aggregates. Since the polarity in the 8F-DeS bilayer was independent of temperature, and as low as that of a typical hydrocarbon surfactant bilayer, hydration of the 8F-B2ES oxyethylene units would increase the polarity, and then loosen the 8F-B2ES packing within the bilayer. This probably led to distortion of the lamellar aggregates.
本研究报道了一种阴离子混合表面活性剂 8F-B2ES 的独特水溶液晶行为，其具有 2-[2-(丁氧基)乙氧基]乙基和 1H,1H,2H,2H-全氟癸基尾链。使用具有无乙氧基单元的 8F-B2ES 类似物混合表面活性剂（8F-DeS）和具有两个 2-(1H,1H,2H,2H-全氟己氧基)乙基尾链的对称氟化双尾表面活性剂（4FEOS）作为对照表面活性剂，以研究乙氧基单元和混合结构对液晶行为的影响。偏光显微镜观察表明，每种表面活性剂/水混合物在表面活性剂浓度高于 10wt.%时都会形成层状液晶相。在 30wt.% 8F-B2ES/水混合物的情况下，在高于 40°C 的温度下观察到两种类型的球形聚集体：一种是具有马耳他十字纹理的典型层状液晶，另一种是各向同性的。有趣的是，当 8F-B2ES 层状相冷却至 40°C 以下时，层状聚集体被扭曲，各向同性液滴变得各向异性。由于这种独特的液晶行为在对照表面活性剂的水混合物中未观察到，因此混合化烃尾中的乙氧基单元在行为中起着重要作用。本研究还通过芘溶解在每个层状相中荧光光谱测量，研究了乙氧基单元对混合表面活性剂双层微环境极性的影响。在 70°C 时，8F-B2ES 双层的极性为烃类表面活性剂层状相的极性，并随着温度的降低逐渐增加。尽管存在层状聚集体，但在 40°C 以下，极性与亲水性球形胶束的极性相同。由于 8F-DeS 双层的极性与温度无关，并且低至典型的烃类表面活性剂双层的极性，因此 8F-B2ES 乙氧基单元的水合会增加极性，然后使双层内的 8F-B2ES 组装松动。这可能导致层状聚集体的变形。
