Consequences of nonergodicity in aqueous binary PEO-PB micellar dispersions
Consequences of nonergodicity in aqueous binary PEO-PB micellar dispersions
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DOI：
10.1021/ma035467j
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发表时间：
2004-02-24
期刊：
影响因子：
5.5
通讯作者：
Bates, FS
中科院分区：
文献类型：
--
作者：
Jain, S;Bates, FS
用低温透射电子显微镜（cryo-TEM）研究了聚环氧乙烷-聚丁二烯（PEO-PB）两嵌段共聚物的胶束水分散体系。通过预混合（分散前）和后混合（分散后）具有不同组成和分子量的二嵌段制备了各种二元共混物。冷冻TEM结果证实，聚集体之间没有可察觉的大分子交换，导致非遍历状态，其中从未达到总体平衡。然而，许多微观图像的分析导致的结论，这些nonergodic胶束放松到局部平衡状态，通过分散过程中建立的拓扑框架内的嵌段共聚物的再分配。不同的平均组成和分子量表现出不同程度的结构复杂性，这似乎在网络形成附近的峰值。远离该条件，胶束形态对核或冠多分散性相对不敏感。然而，在单峰和近单分散的两亲物产生分支蠕虫状胶束和网络的组合物中，双峰混合物显示胶束内分离导致圆柱形起伏和章鱼状聚集体与圆柱形胶束从一个单一的双层核心发出。这些调查结果进行了讨论的背景下，界面曲率和表面活性。
Aqueous micellar dispersions of poly(ethylene oxide)-poly(butadiene) (PEO-PB) diblock copolymers were investigated using cryogenic transmission electron microscopy (cryo-TEM). A variety of binary blends were prepared by premixing (before dispersion) and postmixing (after dispersion) diblocks with varying composition and molecular weight. Cryo-TEM results establish there is no perceptible exchange of macromolecules between aggregates resulting in a nonergodic state, where overall equilibrium is never achieved. However, analysis of many microscopic images leads to the conclusion that these nonergodic micelles relax to a state of local equilibrium through the redistribution of block copolymers within the topological framework established during dispersion. Different average compositions and molecular weights exhibit varying degrees of structural complexity, which appears to peak in the vicinity of network formation. Away from this condition the micelle morphology is relatively insensitive to core or corona polydispersity. However, at compositions where the monomodal and nearly monodisperse amphiphiles produce branched wormlike micelles and a network, bimodal mixtures displayed intramicellar segregation leading to cylindrical undulations and octopus-like aggregates with cylindrical micelles emanating from a single bilayer core. These findings are discussed in the context of interfacial curvature and surfactancy.