Phase behavior and self-organized structures in water/poly(oxyethylene) cholesteryl ether systems
Phase behavior and self-organized structures in water/poly(oxyethylene) cholesteryl ether systems
复制标题
DOI：
10.1021/jp048469u
复制
发表时间：
2004-08-26
影响因子：
3.3
通讯作者：
Kunieda, H
中科院分区：
文献类型：
--
作者：
Sato, T;Hossain, MK;Kunieda, H
与传统的非离子型聚氧乙烯胆固醇醚表面活性剂不同，聚氧乙烯胆固醇醚（ChEO（n））具有大体积的非柔性疏水部分，在水中可形成多种自组装结构。我们通过目视观察、流变仪、小角X射线散射（SAXS）、动态光散射（DLS）、介电弛豫谱（DRS）和密度计研究了水/ChEO（15）和水/ChEO（10）体系的相行为和胶束结构。结果表明，在水/ ChEO（15）体系中，形成了水相胶束（W-m）、Fd 3 m空间群的不连续胶束立方相（I-1）、六方相（H-1）、矩形带状相（R-1）和层状相（L-alpha），而在水/ChEO（10）体系中，在室温下形成了W-m、未知相、R-1、缺陷层状相（L-alpha（H））和L-alpha相。与传统的水性非离子表面活性剂体系相比，中间R-1相区非常宽。对于水/ChEO（15）体系，随着水含量的增加，R-1区的堆积参数P逐渐减小，最后在W-s处收敛到1/2，接近0.58，表明H-1相的形成。R-1相在系统中充当“扭曲的”六方相。而在水/ChEO（10）体系中，随着W-S的减小，P呈阶梯状增加，在W-S接近0.7时达到最大值约0.67，正好对应于不连续和双连续结构的临界值。之后，P随着Ws的减小而减小，并且在类似于0.5的W-S处出现不能索引到液晶相的任何已知空间群的未知相。W-m溶液SAXS数据的GIFT分析表明，在环境温度范围内，水/ChEO 15体系中存在球形胶束，但ChEO（10）在水中形成短棒状胶束。在水/ChEO 10体系中，随着温度的升高，棒状胶束逐渐长大，形成粘弹性胶束相。DRS计算得到的各水合单元的水合数近似为4，这与DLS计算得到的Wm相的表观流体动力学半径的浓度依赖性一致。水合水分子应被视为胶束的组成部分。在水/ChEO（n）体系中的这些新相行为的特征中的大多数是基于ChEO（n）的非柔性和庞大的疏水部分。
Different from conventional nonionic poly(oxyethylene) surfactants, poly(oxyethylene) cholesteryl ethers, ChEO(n), possess a bulky and nonflexible hydrophobic part and form a variety of self-organized structures in water. We investigated the phase behavior and the micellar structures in the water/ChEO(15) and water/ChEO(10) systems by means of visual observation, rheometry, small-angle X-ray scattering (SAXS), dynamic light scattering (DLS), dielectric relaxation spectroscopy (DRS), and densimetry. We found that in the water/ ChEO(15) system, aqueous micellar (W-m), discontinuous micellar cubic (I-1) with Fd3m space group, hexagonal (H-1), rectangular ribbon (R-1), and lamellar (L-alpha) phases are formed, whereas W-m, unknown, R-1, defected lamellar (L-alpha(H)), and L-alpha phases are produced in the water/ChEO(10) system at ambient temperatures. Compared with a conventional aqueous nonionic surfactant system, the intermediate R-1 phase region is incredibly wide. As for the water/ChEO(15) system, with increasing water content, the packing parameter, P, in the R-1 region is gradually decreased, finally converging to 1/2 at W-s similar to 0.58, indicative of the formation of the H-1 phase. The R-1 phase acts as a "distorted" hexagonal phase in the system. However, in the water/ChEO(10) system, upon reduction of W-S, P shows a steplike increase and the maximum value similar to0.67 at W-S similar to 0.7, just corresponding to the threshold of discontinuous and bicontinuous structures. After that, P is decreased with decreasing Ws and unknown phase that cannot be indexed to any known space group for liquid crystalline phases emerges at W-S similar to 0.5. The GIFT analysis of the SAXS data for the W-m solution indicates that spherical micelles are present in the water/ChEO15 system in an ambient temperature range, but ChEO(10) forms a short-rod micelle in water. With increasing temperature, rodlike micelles appear to be grown and a viscoelastic micellar phase is formed in water/ChEO10 system. The hydration number for each oxyethylene unit is evaluated as similar to4 by DRS, which gives a consistent explanation for the concentration dependence of the apparent hydrodynamic radius in the Wm phase obtained by DLS. Hydrated water molecules should be regarded as a constituent of the micelles. The majority of these features of novel phase behavior in the water/ChEO(n) systems are based on a nonflexible and bulky hydrophobic part of ChEO(n).