【作者】 王立权；

【导师】 林嘉平；

【作者基本信息】 华东理工大学 ， 材料科学与工程， 2011， 博士

【摘要】 多尺度结构是由分子聚集而成的聚集体在较大尺度上再次聚集,然后以类似的方式依次在不同的尺度上不断聚集而最终形成的结构中有结构的组装体。共聚物的多尺度微相结构是自组装研究领域的一个重要的方向。多尺度结构的自组装可以满足对多功能材料的需求,并实现仿生材料的构筑。本论文以自洽场理论为主要工具,随机相近似和耗散粒子动力学模拟等为辅助手段,研究了由共聚物自组装形成的纳米尺度上分级的多尺度微相结构。共聚物分子构型包括线性多嵌段共聚物、支化嵌段共聚物以及纳米粒子杂化共聚物等。研究内容包括“共聚物在本体中形成的多尺度微相结构”和“共聚物在稀溶液中形成的多尺度微相结构”两部分。在本体中,通过利用四阶向后差分方法求解自洽场扩散方程,成功地研究了由共聚物在强分凝条件下自组装形成的平行和垂直排列的多尺度结构,模拟结果与实验吻合,并预测了一系列新的结构；在稀溶液中,提出了多核胶束的概念并用自洽场理论证实疏-亲-疏线性三嵌段共聚物具有形成诸如超分子螺旋胶束之类的多核胶束的能力,揭示了由接枝共聚物形成的多尺度囊泡的稳定性及其多级的自组装过程,并探索了纳米粒子杂化共聚物的稀溶液自组装行为。1.共聚物在本体中形成的多尺度微相结构1) A(BC)n多嵌段共聚物形成的多尺度微相结构A(BC)n多嵌段共聚物可以自组装形成一系列多尺度微相结构,如层中有层等。大尺度结构通过A链段和(BC)n链段间的微相分离形成,而小尺度结构由B、C链段的自组装形成。通过改变4链段长度可以得到不同类型的多尺度结构,随着A链段长度的增加,由A链段形成的微区结构由球状变成柱状,再变成层状,最后变成基质；而由B、C链段形成的小尺度结构始终保持层状。链段间的分凝强度对多尺度结构也有影响。当A、B间的分凝强度小于A、C间的分凝强度时,A(BC)n多嵌段共聚物始终形成大、小尺度结构相互平行的多尺度结构；反之,其形成的多尺度结构较为复杂,当B、C间的分凝强度增大到-定值时,大、小尺度结构间的排列方式由平行转变为垂直。2)线性-梳状嵌段共聚物形成的多尺度微相结构除了三组分的A(BC)n多嵌段共聚物,二组分的线性-梳状嵌段共聚物同样能够自组装形成多尺度结构,如平行和垂直的层中有层等。大尺度结构通过线性链段和梳状链段间的微相分离形成,而小尺度结构由梳状链段内部的主链和侧链间的微相分离形成。改变线性链段长度,既可以改变大尺度结构的形貌,也可以改变小尺度结构的形貌。此外,改变链段间的分凝强度也会引起多尺度结构的形貌以及排列方式的改变。3)多侧链接枝共聚物的微相分离鉴于线性-梳状嵌段共聚物的接枝共聚物特性,研究了多侧链接枝共聚物的自组装行为。通过随机相近似计算,发现当接枝点的位置和数量比较大时,侧链数量对旋节线影响很小,接枝共聚物表现出线性-梳状嵌段共聚物的特性。此外,利用自洽场理论计算构筑了一系列单尺度结构的相图。随着侧链数量的增加,有序-有序相边界向主链体积分数增大的方向偏移,而且有序结构的周期减小,界面宽度增加。2.共聚物在稀溶液中形成的多尺度结构1)疏-亲-疏线性ABC三嵌段共聚物的稀溶液自组装在稀溶液中,具有亲溶剂的中间链段和疏溶剂的末端链段的线性ABC三嵌段共聚物能够自组装形成诸如超分子螺旋胶束之类的多尺度结构。该多尺度结构具有不同于多舱胶束的特征,因而提出了多核胶束的概念。研究发现,链段的长度和溶解度对多核胶束有很大影响。通过同实验结果比较,发现模拟结果不但能够重复实验现象,而且能够解释实验现象。2)接枝共聚物在主链友好型溶剂中的自组装除了三组分共聚物,二组分接枝共聚物在主链友好型溶剂中同样能够自组装形成多尺度微相结构,如多层囊泡和复合囊泡等。采用自洽场理论和耗散粒子动力学模拟分别研究了多尺度结构的热力学和动力学行为。自洽场理论的研究表明,由接枝共聚物形成的多尺度囊泡是热力学稳定的,其形成与链段间的分凝强度以及链段的溶解性相关；而耗散粒子动力学的模拟发现,多尺度囊泡的形成过程是分级的,它依赖于一系列中间态的形成。3)纳米粒子杂化共聚物的稀溶液自组装除了柔性共聚物,纳米粒子杂化共聚物在稀溶液中也能自组装形成多尺度结构。这一共聚物的稀溶液自组装不但涉及到柔性嵌段间的自组装,而且涉及到纳米粒子间的自组装。类似于柔性共聚物的稀溶液自组装,由纳米粒子杂化共聚物形成的多尺度结构依赖于聚合物链段的长度以及聚合物链段与纳米粒子的相容性。本论文有助于拓宽人们对于自组装的认识,有助于理解多尺度结构的形成机理；为实验科学提供必要的理论支持,并指导和促进多尺度结构的进一步设计和制备；此外,希望本论文有助于多尺度结构的拓展和应用,比如光电装置、多功能响应性材料以及多尺度复合材料的制备等,并方便科研工作者找到合适的材料样本。更多还原

【Abstract】 Hierarchical structures are assemblies of molecules or their aggregates that are intertwined with other phases, which in turn are similarly organized at increasing length levels. Study of hierarchical structures is central to the field of self-assembly. The self-assembly of hierarchical structures can provide excellent candidates of materials designed for multifunctional applications and bring us one-step closer to achieve natural assembly. In this dissertation, we directed towards the study of the structures with hierarchy at nanoscale, i.e., hierarchical microstructure, by using self-consistent field theory and other theoretical methods. The dissertation was organized into two main sections, including hierarchical microstructure in bulk and hierarchical microstructure in dilute solution. In bulk, by solving diffusion equations with fourth-order backward differentiation formula, we successfully discovered a series of microstructures that existed at higher interaction strength. The calculations can not only reproduce the experimental results, but also predict various new hierarchical microstructures. In selective solvents, we proposed a concept of multcore micelles and further confirmed that the linear terpolymers are capable of forming multicore micelles. Furthermore, we discovered a variety of hierarchcal vesicles with hierarchical self-assembly process in graft copolymer solutions, and various hybrid aggregates in the solution of nanoparticle tethered block copolymers.1. Hierarchical Microstructures Self-Assembled from Copolymers in Bulk1) Hierarchical Microstructures Self-Assembled from A(BC)n Multiblock CopolymerA(BC)n multiblock copolymer are capable of self-assembling into various hierarchical microstructures such as lamellae-in-lamella. In the hierarchical microstructures, the large-length-scale structures were formed by the separation between A blocks and (BC)n blocks, while the small-length-scale structures were obtained by the separation between B and C blocks. The hierarchical microstructures can be tuned by changing the A block length. As A block length increases, the A domain can be changed from sphere to cylinder, then to lamella, and finally to matrix, while the small-length-scale structures still remain lamella. In addition, the interaction strength between each blocks have an influence on the hierarchical structures. When the interaction strength between A and B blocks is smaller than that between A and C blocks, the small structures and the large structures in hierarchical microstructures are packed in parallel; in reverse, the hierarchical structure become more complex, where the small structure are arranged perpendicular to the large structures as the interaction strength between B and C blocks is significantly high.2) Hierarchical Microstructures Self-Assembled from Coil-Comb Block CopolymersIn addition to ternary copolymers, binary coil-comb block copolymers are able to self-assemble into hierarchical microstructures including parallel and perpendicular lamellae-in-lamella. The large-length-scale structures are formed by the sparation between coil blocks and comb blocks, whereas the small-length-scale structures are obtained by the self-assembly within the comb blocks. The variation of the coil block length can not only change the large-length-scale structure, but also the small-length-scale structures. Furthermore, the change of interaction strength can lead to a change of the hierarchical microstructures.3) Microphase Saparation in Multigraft Copolymer MeltsBecause of the nature of coil-comb block copolymer, the phase behavior of multigraft copolymers was also investigated. The study of random phase approximation reveals that the spinodals are independent of the junction number and junction position as the junction number and junction position are large enough. In this sense, the graft copolymers perform as the coil-comb block copolymers. Using the self-consistent field theory, phase diagrams of the conventional structures were also mapped out.2. Hierarchical Microstructrues Self-assembled from Copolymers in Dilute Solution1) Self-Assembly of Linear ABC Terpolymers in B-Selective SolventsIn selective solvents, linear ABC terpolymer combining a solvophilic midblock and two mutually imcompatible solvophobic endblocks are capable of self-assembling into hierarchical microstructures like superhelix. The characteristic of these hierarchical microstructures is different from the multicompartment micelles, and therefore a concept of multicore micelles was proposed. The length and solubility of the blocks shows a pronounced effect on the morphology of multicore micelles. The theoretical calculations not only reproduced the experimental results, but also provided a deep insight into the experimental phenomena.2) Self-Assembly of Graft Copolymers in Backbone-Selective SolventsIn addition to ternary copolymers, binary graft copolymer can also self-assemble into hierarchical microstructures in a backbone-selective solvent. The example of hierarchical microstructures includes multilamellar vesicles and large-compound vesicles. The self-consistent field calculations revealed that the hierarchical vesicles are thermodymic stable. The formation of hierarchical vesicles depends on the solubility of blocks as well as the interaction strength between backbone and graft arms. The dissipative particle dynamics simulations demonstrated that the self-assembly process of the hierarchical vesicle is hierarchical, depending on the formation of multiple intermediate structures.3) Self-Assembly of Nanoparticle Tethered Block Copolymers in Dilute SolutionIn addition to flexible copolymers, nanoparticle tethered block copolymers are capable of self-assembling into hierarchical microstructures in selective solvents. The self-assembly of nanoparticle tethered block copolymers involve not only the microphase separation between different blocks, but also the close packing of nanoparticles. Similar to flexible copolymers, the self-assembled microstructures are dependent of the block lengths as well as the incompatibility between polymeric blocks and nanoparticles.The study is helpful for expanding the morphological window of copolymers and understanding the self-assembly mechanism of hierarchical microstructures. The results provided a theoretical support for the experiments and further guide the future experiments. The work is anticipated to facilitate the application of hierarchical materials, such as the design of photovoltaic devices, the development of materials with enhanced mechanical response, and the production of hierarchical organic/inorganic hybrid nanocomposites.更多还原