【作者】 孔维新；

【导师】 李宝会；

【作者基本信息】 南开大学 ， 凝聚态物理， 2010， 博士

【摘要】 在纳米技术领域,“自下而上”制造结构材料的方法之一是利用大分子的自发组装。人们认为双亲分子自组装形成的超分子和有序结构可以用于开发很多新型纳米技术的应用。“自下而上”方法成功的关键是能够预测和控制分子自组装所形成的纳米结构。在制造纳米尺度模版方面,一类非常有前景的分子是嵌段共聚物,它们是由两种或者多种化学性质不同的均聚物通过共价键连接而成的大分子。近年来的研究显示通过调节嵌段长度,共聚物链结构和单体的类型,嵌段共聚物可被用于设计很多具有奇特结构的材料。嵌段共聚物在选择性溶剂中的自组装具有重要意义,因为它能形成不同形状和不同内部结构的胶束,从而为制造具有纳米结构的材料提供了众多的途径。特别是嵌段共聚物形成多相分隔胶束标志着向获取具有多功能和在若干长度尺度上可设计结构特征的多级自组装迈出了重要的一步。在本论文中,我们用模拟退火方法对三嵌段共聚物的溶液态自组装进行了系统研究：考察了不同参数对胶束形态和形状的影响；观察到多种多相分隔胶束；分析了嵌段共聚物链在一些典型胶束中的排列方式。论文第一章对嵌段共聚物的背景、研究中所使用的模型和方法、和论文的框架做了简要介绍。论文第二章对双亲星形ABC三嵌段共聚物溶液的自组装进行了系统研究。杂链星形三嵌段共聚物在溶剂中的自组装为获得多相分隔胶束提供了一条便捷而有效的途径。模拟中我们发现了丰富的多相分隔胶束；构建了典型星形三嵌段共聚物体系的相图。我们发现胶束的整体形态在很大程度上由亲溶剂A-支链的体积分数控制,而内部相分离结构则依赖于两种斥溶剂支链(B和C)的体积分数比。嵌段-溶剂和嵌段-嵌段之间的相互作用可用于调控A-支链的有效体积分数从而可导致胶束形态的转变。在B和C两斥溶剂支链长度相等的三嵌段共聚物体系中,观察到几种新型胶束,包括：具有横向结构(螺旋或堆叠的圆环)的囊泡、节形半囊泡,和椭圆形或三角形片层。当B和C支链的长度不相等时,观察到多相分隔的圆盘和洋葱等新型胶束结构。第三章研究了双亲线形三嵌段共聚物的溶液态自组装行为。考察了共聚物的组分、嵌段-溶剂和嵌段-嵌段之间的相互作用对胶束形态和形态转变的影响。首先,我们研究了线形ABC三嵌段共聚物在对其中间的B-嵌段具有选择性的溶剂中的自组装行为。通过将大量的模拟结果与星形ABC三嵌段共聚物或AB、BC两嵌段共聚物所形成的胶束形态对比,我们发现亲溶剂B-嵌段对斥溶剂微区的空间分布和形状的限制非常明显。随着增加两种斥溶剂嵌段之间的不相容性,在高浓度的共聚物体系中观察到大量的复杂胶束,如囊泡、多层的大囊泡、复杂网络笼状胶束和平面网络胶束等。我们还对线形ABA三嵌段共聚物在对中间B-嵌段具有选择性的溶剂中的自组装行为进行了研究。我们发现随着A-嵌段和溶剂之间的相互作用强度的不断增加,体系依次形成球状、柱状、圆环状、圆盘状、网络笼状胶束和囊泡。通过改变A-嵌段和溶剂之间的相互作用和体系的浓度,我们构建了两种具有不同组分的嵌段共聚物体系的胶束形态相图。发现溶液浓度的增高可以使体系形成复杂形态的胶束。随后,我们对线形ABC三嵌段共聚物在对其一端嵌段具有选择性的溶剂中的自组装行为进行了研究。通过改变斥溶剂A-嵌段的体积分数,我们在体系中观察到丰富的奇特胶束结构；我们发现两种斥溶剂嵌段(A和B)之间的体积分数比的增大可以使胶束的形态从核-壳-冠结构转变到树梅状,此外,体系的浓度控制着胶束形态的复杂性。胶束的详细内部结构取决于两种斥溶剂嵌段之间的不容性。我们发现亲溶剂的C-嵌段通过控制三嵌段共聚物链的排列方式和其在胶束中的位置,在很大程度上决定着胶束的形态。最后,我们对由线形ABC三嵌段共聚物在对其两端A-和C-嵌段都具有选择性的溶剂中所形成的胶束进行了研究。通过跟AB或ABA嵌段共聚物形成的胶束进行对比,我们发现三种体系中胶束形态和形态转变的相似性源于嵌段共聚物仅包含一条斥溶剂嵌段。第四章研究了线形ABC三嵌段共聚物在对其三个嵌段都排斥的溶剂中的自组装行为。我们对共聚物三个嵌段的体积分数、嵌段之间的不相容性和溶剂性质对胶束形态的调控进行了系统的考察。我们观察到大量奇特的胶束形态和若干个形态转变。模拟结果显示胶束的结构和形状在很大程度上由嵌段共聚物的组分、嵌段之间的不容性和溶剂性质之间的竞争控制。更多还原

【Abstract】 One of the bottom-up strategies of creating structured materials for nanotechnology is to utilize spontaneous self-assembly of macromolecules. It has been proposed that the self-assembly of amphiphilic molecules into supramolecular assemblies and ordered structures can be used in the development of many new nanotechnological applications. The key to the success of this bottom-up strategy is the ability to predict and control the self-assembled nanostructures from the building molecules. One promising class of building molecules for nano-scale templates is block copolymers, which are macromolecules formed by covalently linking two or more chemically distinct polymeric blocks. In recent years, it has been demonstrated that block copolymers can be used to engineer a host of novel structures by tuning the block lengths, polymer architecture, and the type of monomers.The self-assembly of block copolymers in selective solvents is of fundamental interest because it offers tremendous promises for the creation of nano-structured materials in the form of micelles of different shape and internal structure. Especially, the possibility of forming multi-compartment micelles from block copolymers represents a significant step toward achieving hierarchical self-assembly with multiple functions and designed architectural features at several length scales. In this thesis, we report an extensive investigation of the solution-state self-assembly of amphiphilic terpolymers using computer simulations with simulated annealing technique. We have studied the influence of different parameters on the resulting micelle structures. A lot of multi-compartment micelles are observed. We have analyzed the chain packing in some representative micelles.Chapter 1 contains a brief introduction of the background of block copolymers, of the model and method used in the research, and of the framework of the thesis.Chapter 2 focuses on studies of self-assembly of ABC star terpolymers. Solution-state self-assembly of miktoarm star terpolymers provides a versatile and powerful route to obtain multi-compartment micelles. A variety of multi-compartment micelles are predicted from the simulations. Phase diagrams for typical star terpolymers are constructed. It is discovered that the overall micelle morphology is largely controlled by the volume fraction of the solvophilic A-arms, whereas the internal compartmented and/or segregated structures depend on the ratio between the volume fractions of the two solvophobic arms. The polymer-solvent and polymer-polymer interactions can be used to tune the effective volume fraction of the A-arm, and thereby induce morphological transitions. For terpolymers with equal or nearly equal length of B and C arms, several previously unknown structures, including vesicles with novel lateral structures (helices or stacked donuts), segmented semi-vesicles, and elliptic or triangular bilayer sheets, are discovered. When the lengths of B and C arms are not equal, novel micelles such as multi-compartment disks and onions are observed.Chapter 3 focuses on studies of solution-state self-assembly of linear triblock copolymers. The effects of polymer composition, polymer-solvents and polymer-polymer interaction on micellar morphology and morphological transitions are extensively investigated.First, the self-assembly of ABC linear terpolymers in solvents selective for the middle B-block is studied. We compared our results with those from ABC star terpolymers, and those from AB, BC diblock copolymer blending system. It is found that the spatial limitation of the middle solvophilic polymer on solvophobic sub-domains is conspicuous. With increasing the incompatibility between solvophobic polymers, a variety of complex morphologies such as vesicles, core containing vesicles, complex net-cage micelles and planar network micelles are observed in high copolymer concentration system. Furthermore, in high copolymer concentration system, ABC linear terpolymers can form complex micelles such as a big micelle contains several small micelles and a big vesicle with several layers.The self-assembly of ABA linear triblock copolymers in solvents selective for the middle B-block is also studied. The simulations reveal that a micellar sequence, ranging from spherical, rodlike, toroidal, disklike micelles, net-cage micelles to vesicles are always formed from the ABA copolymers in different systems, with increasing the A-solvent interactions. Phase diagrams are constructed by varying the A-solvent interaction and terpolymer concentration. It is demonstrated that higher terpolymer concentration can make the system to form complex micelles. A host of complex micellar morphologies and morphological transition are observed. Then, the self-assembly of ABC linear triblock copolymers in solvents selective for one end (C)-block is studied. A variety of novel micellar structures are discovered by varying the volume fraction of solvophobic A-polymer. It is found that the increase of the ratio of the volume fraction between two solvophobic polymers(A and B) can tune the micellar morphology from core-shell-corona structure to raspberry like micelles, and the copolymer concentration can control the complexity of the micelles. The detail structures are determined by the incompatibility between two solvophobic polymers. We found that the solvophilic C-polymer can largely determine the micellar morphology by controlling the packing (direction and location) of terpolymers.Finally, we studied the self-assembly of ABC linear triblock copolymers in solvents selective for the two end blocks. We also compared these results with those from AB and BAB block copolymers. It is found that the similarity of the morphologies among them is caused by the number of the solvophobic block in a copolymer.Chapter 4 focuses on the self-assembly of ABC linear triblock copolymers in solvents which are poor to all of the three blocks. The effects of the volume fraction of the three blocks, of the incompatibilities among different blocks and of the solvent quality on micellar morphology are examined systematically. A variety of novel micellar morphologies and several morphological transitions are discovered. It is revealed that the shape and structure of micelles are controlled by both of the terpolymer composition and the competition between solvent quality and the incompatibility between two solvophobic blocks.更多还原