Castelletto V, Parras P, Hamley I W, Bäverbäck P, Pedersen J Skov, Panine P
Department of Chemistry, University of Reading, Reading, UK.
Langmuir. 2007 Jun 19;23(13):6896-902. doi: 10.1021/la700382y. Epub 2007 May 25.
The self-assembly into wormlike micelles of a poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) triblock copolymer Pluronic P84 in aqueous salt solution (2 M NaCl) has been studied by rheology, small-angle X-ray and neutron scattering (SAXS/SANS), and light scattering. Measurements of the flow curves by controlled stress rheometry indicated phase separation under flow. SAXS on solutions subjected to capillary flow showed alignment of micelles at intermediate shear rates, although loss of alignment was observed for high shear rates. For dilute solutions, SAXS and static light scattering data on unaligned samples could be superposed over three decades in scattering vector, providing unique information on the wormlike micelle structure over several length scales. SANS data provided information on even shorter length scales, in particular, concerning "blob" scattering from the micelle corona. The data could be modeled based on a system of semiflexible self-avoiding cylinders with a circular cross-section, as described by the wormlike chain model with excluded volume interactions. The micelle structure was compared at two temperatures close to the cloud point (47 degrees C). The micellar radius was found not to vary with temperature in this region, although the contour length increased with increasing temperature, whereas the Kuhn length decreased. These variations result in an increase of the low-concentration radius of gyration with increasing temperature. This was consistent with dynamic light scattering results, and, applying theoretical results from the literature, this is in agreement with an increase in endcap energy due to changes in hydration of the poly(ethylene oxide) blocks as the temperature is increased.
通过流变学、小角X射线和中子散射（SAXS/SANS）以及光散射研究了聚环氧乙烷-聚环氧丙烷-聚环氧乙烷三嵌段共聚物普朗尼克P84在盐水溶液（2M NaCl）中自组装成蠕虫状胶束的过程。通过控制应力流变仪测量流动曲线表明在流动下会发生相分离。对经受毛细管流动的溶液进行的小角X射线散射显示，在中等剪切速率下胶束会排列，不过在高剪切速率下会观察到排列的丧失。对于稀溶液，未排列样品的小角X射线散射和静态光散射数据在散射矢量的三个数量级上可以叠加，提供了关于蠕虫状胶束结构在几个长度尺度上的独特信息。小角中子散射数据提供了关于更短长度尺度的信息，特别是关于胶束冠层的“团块”散射。这些数据可以基于具有圆形横截面的半柔性自回避圆柱体系统进行建模，如具有排除体积相互作用的蠕虫状链模型所描述的那样。在接近浊点（47摄氏度）的两个温度下比较了胶束结构。发现在该区域胶束半径不随温度变化，尽管轮廓长度随温度升高而增加，而库恩长度减小。这些变化导致低浓度回转半径随温度升高而增加。这与动态光散射结果一致，并且应用文献中的理论结果，这与随着温度升高聚环氧乙烷嵌段水化变化导致端帽能量增加是一致的。
