Frustrated Phases of Block Copolymers in Nanoparticles
Frustrated Phases of Block Copolymers in Nanoparticles
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DOI：
10.1002/anie.200803003
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发表时间：
2008-01-01
影响因子：
16.6
通讯作者：
Shimomura, Masatsugu
中科院分区：
文献类型：
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作者：
Higuchi, Takeshi;Tajima, Atsunori;Shimomura, Masatsugu
嵌段共聚物的微相分离结构作为构建纳米尺度结构的新型结构单元引起了人们极大的兴趣。在嵌段共聚物膜中，各种类型的微相分离结构（例如，圆柱形，层状，双连续的，和其他），这取决于嵌段共聚物的链段比和分子量，已被报道。[1]微相分离结构已被应用于光刻的蚀刻掩模，[2]金属阵列的形成，[3]光子晶体，[4，5]和激光器件，[6]因为嵌段共聚物通过简单的制备过程形成高度有序的纳米级结构，如旋涂。聚合物纳米粒子由于其在光学、电子学和生物学方面的潜在应用，在纳米科学和纳米技术领域也受到了广泛的关注。[7]特别地，具有特定内部结构的纳米颗粒可以应用于从其内部结构衍生的功能材料。例如，两亲性嵌段共聚物胶束（其为核-壳型颗粒）用作药物递送系统中的载体。[8]嵌段共聚物纳米粒子具有微相分离结构，如柱状和层状结构，具有独特的化学和物理性质。然而，有一些报告的形成嵌段共聚物颗粒的圆柱形，层状，和其他微相分离结构。[9，10]嵌段共聚物颗粒的制备难以用用于制备聚合物颗粒的常规方法，例如乳液聚合。[11我们已经报道了各种聚合物纳米颗粒可以通过简单的溶剂蒸发过程来制备，即，从含有不良溶剂和良好溶剂的聚合物溶液中蒸发良好溶剂;该技术被称为SORP（自组织沉淀）方法。[13]该方法可通过选择用于聚合物的合适溶剂组合而应用于各种聚合物。例如，在其膜中形成层状结构的疏水性二嵌段共聚物在纳米颗粒中形成单向堆叠的层状和洋葱状结构。[14本文报道了嵌段共聚物分子量对纳米颗粒中微相分离结构的影响。通过使用SORP方法，从具有各种各样的分子量的嵌段共聚物制备纳米颗粒，从30 000到150万。具有大分子量（> 20万）的嵌段共聚物形成具有独特微相分离结构（例如Janus型、网球状、蘑菇状、轮状和螺旋状结构）的纳米颗粒，即使它们的膜仅形成层状结构。扫描透射电子显微镜（STEM）的观察表明，在纳米粒子的微相分离结构是依赖于纳米粒子的直径。从纳米粒子的限制效应出发，讨论了粒子直径与微相分离结构之间的关系。[16采用SORP方法从不同分子量的嵌段共聚物制备纳米粒子，研究了嵌段共聚物分子量对纳米粒子微相分离结构的影响。所用的含有聚苯乙烯（PSt）和聚异戊二烯（PI）链段的嵌段共聚物汇总于表1中。这些嵌段共聚物形成具有层状结构的膜。将每种嵌段共聚物溶解在四氢呋喃（THF）中，并以0.
Microphase separation structures of block copolymers have attracted much interest as novel building blocks for the creation of nanometer-scale structures. In block copolymer films, various kinds of microphase separation structures (eg, cylindrical, lamellar, bicontinuous, and others), which are dependent on the segment ratio and molecular weight of the block copolymer, have been reported.[1] Microphase separation structures have been applied to etching masks for lithography,[2] the formation of metal arrays,[3] photonic crystals,[4, 5] and laser devices,[6] because block copolymers form highly ordered nanoscale structures through simple preparation processes, such as spin coating. Polymer nanoparticles have also received much attention in the fields of nanoscience and nanotechnology, because of their potential in optical, electronic, and biological applications.[7] In particular, nanoparticles with specific internal structures can be applied to functional materials derived from their internal structures. For example, amphiphilic block copolymer micelles, which are core–shell-type particles, are used as carriers in drug-delivery systems.[8] Block copolymer nanoparticles with microphase separation structures, such as cylindrical and lamellar structures, could possess unique chemical and physical properties. However, there are a few reports of the formation of block copolymer particles with cylindrical, lamellar, and other microphase separation structures.[9, 10] The preparation of block copolymer particles is difficult with conventional methods for the preparation of polymer particles, such as an emulsion polymerization.[11, 12] We have reported that various kinds of polymer nanoparticles can be prepared by a simple solvent-evaporation process, that is, the evaporation of a good solvent from a polymer solution containing poor and good solvents; this technique is known as the SORP (self-organized precipitation) method.[13] This method can be applied to various polymers by selecting suitable solvent combinations for the polymers. For example, a hydrophobic diblock copolymer, which forms lamellar structures in its film, formed onedirectionally stacked lamellar and onionlike structures in the nanoparticles.[14, 15]Herein we report the investigation of the effect of the molecular weight of block copolymer on the microphase separation structures in nanoparticles. Nanoparticles were prepared from block copolymers with a wide variety of molecular weights, ranging from 30 000 to 1.5 million, by using the SORP method. Block copolymers with large molecular weight (> 0.2 million) formed nanoparticles with unique microphase separation structures (eg, Janus-type, tennisball-, mushroom-, wheel-, and screwlike structures), even though their films formed only lamellar structures. Scanning transmission electron microscopy (STEM) observations revealed that the microphase separation structures in the nanoparticles are dependent on the diameters of the nanoparticle. The relationship between particle diameter and the microphase separation structures is discussed in terms of the confinement effect in nanoparticles.[16, 17] Nanoparticles were prepared from block copolymers with a wide variety of molecular weights by using the SORP method to study the effect of the molecular weight of block copolymer on the microphase separation structures in the nanoparticles. The block copolymers employed, which contained polystyrene (PSt) and polyisoprene (PI) segments, are summarized in Table 1. These block copolymers form films with lamellar structures. Each block copolymer was dissolved in tetrahydrofuran (THF), and polymer solutions were prepared at a concentration of 0 …