Multiple morphologies and characteristics of ''crew-cut'' micelle-like aggregates of polystyrene-b-poly(acrylic acid) diblock copolymers in aqueous solutions
Multiple morphologies and characteristics of ''crew-cut'' micelle-like aggregates of polystyrene-b-poly(acrylic acid) diblock copolymers in aqueous solutions
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DOI：
10.1021/ja953709s
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发表时间：
1996-04-03
影响因子：
15
通讯作者：
Eisenberg, A
中科院分区：
文献类型：
--
作者：
Zhang, LF;Eisenberg, A
用透射电子显微镜研究了聚苯乙烯-b-聚丙烯酸、PS-b-PAA、两嵌段共聚物在近平衡条件下形成的不同形态的平切胶束状聚集体。共聚物中不溶嵌段(PS)含量在80~98wt%之间。在球形胶束中，PS嵌段聚集形成的胶束核一般是单分散的。星形胶束和螺旋形胶束的比较表明，后者的区别在于核表面的电晕链密度低，核中PS块的伸展程度低。随着嵌段共聚物中PAA含量的减少，聚集体的形态逐渐由球状向圆柱状、双层(囊泡和片状)转变，最终形成由亲水性表面包围的倒置胶束组成的复合胶束。这种复合胶束被认为是嵌段共聚物的一种新的形态。均聚苯乙烯的加入改变了双嵌段的形态，使其由双层或圆柱状变为球状。本系统提供了第一个实例，在具有变化的共聚物组成的低分子量溶剂中，可以直接观察到嵌段共聚物中的所有这些多重聚集形态。人们认为，这是目前为止制备稳定的嵌段共聚物纳米级玻璃微囊的唯一方法，这些微泡可以自发形成，可以在水中分离并直接用电子显微镜进行研究。
Crew-cut micelle-like aggregates of various morphologies prepared from polystyrene-b-poly(acrylic acid), PS-b-PAA, diblock copolymers under near-equilibrium conditions, were studied by transmission electron microscopy (TEM). The insoluble block (PS) contents in the copolymers ranged from 80 to 98 wt %. In spherical micelles, the micelle cores, formed by aggregation of the PS blocks, were generally monodisperse. A comparison between star and crew-cut micelles showed that the latter are distinguished by a low density of corona chains on the core surface and a low degree of stretching of the PS blocks in the cores. As the PAA content in block copolymer decreased, the morphology of the aggregates changed progressively from spheres to cylinders, to bilayers (both vesicles and lamellae), and eventually to compound micelles consisting of an assembly of inverted micelles surrounded by a hydrophilic surface. The compound micelles are believed to be a new morphology for block copolymers. The addition of homopolystyrene to the diblocks changed the morphologies from bilayers or cylinders to spheres. The present system provides the first instance in which all these multiple aggregate morphologies have been observed directly in block copolymers in a low molecular weight solvent with changing copolymer composition. It is believed that this is the only way so far to prepare stable nanosize glassy vesicles of block copolymers which form spontaneously and can be isolated in water and studied directly by electron microscopy.