【作者】 王艳；

【导师】 黄建花；

【作者基本信息】 浙江理工大学 ， 应用化学， 2010， 硕士

【摘要】 近年来,合成形态、大小及结构可人为调控的无机材料成为现代材料科学的一个重要研究方向。大量的实验结果表明,嵌段共聚物对无机晶体的结晶、生长以及由纳米颗粒到各种特殊超结构的形成过程均有独特的影响。但是目前合成得到的材料主要还是形貌上的创新,对晶体生长机理及各种纳米超结构的形成机理的认识还不统一,计算机模拟和理论研究鲜有报导。本论文利用键长涨落Dynamic Monte Carlo方法对嵌段共聚物囊泡结构的形成机理进行了较详细的模拟研究,同时考察了嵌段共聚物与疏水纳米颗粒的共存体系。论文的研究内容主要包括三部分:（1）两亲嵌段共聚物囊泡的形成机理研究;（2）考察形成囊泡的影响因素;（3）考察嵌段共聚物对纳米颗粒聚集行为的影响。全文共分六章:第一章文献综述,主要介绍两嵌段共聚物“平头型”聚集体的形成及影响因素,以及嵌段共聚物在无机材料合成方面的应用。对计算机模拟方面已得到的研究成果也进行了简单介绍。第二章介绍Monte Carlo模拟方法的基本原理及在高分子科学中的应用,并对本论文中所用的模型及方法进行了说明。第三章详细讨论两亲嵌段共聚物囊泡的形成机理。两亲嵌段共聚物分子用A_mB_n表示,其中A链段疏水、B链段亲水。在只考虑A-A链段之间的相互吸引作用时(ε_AA = -1.0),模拟结果发现对于（m + n）≤6的两嵌段共聚物链,只有n = 1的链结构才能形成囊泡。对于A₃B₁型嵌段共聚物,在2%～15%的链节浓度范围内都可以得到单一的囊泡结构。A链段组成囊泡壁,B链段分布在囊泡的内、外表面。通过考察囊泡的动力学形成过程,我们发现囊泡由板状的胶束经过卷曲闭合而成。该卷曲机理曾在分子动力学（MD）、耗散粒子动力学（DPD）、布朗动力学（BD）等模拟研究中观察到,但对于格点模型,属首次发现。第四章考察A_mB₁型嵌段共聚物囊泡的影响因素。发现在m≥3时,A_mB₁链都可以自组装成囊泡结构。浓度是影响A₂B₁共聚物能否形成囊泡比较关键的因素。对于A₃B₁型囊泡,随着链节浓度的增加,囊泡体积逐渐变大,空腔中包含的溶剂量也随之增加。最后考察了溶剂效应,在考虑A-A之间的相互吸引条件下,同时考虑A链段与溶剂的排斥作用ε_AS。结果发现:当ε_AS较小时,A₃B₁链通过板卷曲机理形成囊泡;当ε_AS≥0.05时,A₃B₁链通过扩散机理形成囊泡。而且囊泡尺寸随着ε_AS的增加而减小,表明我们可以通过调节溶剂性质,来调控囊泡尺寸。通过对链段结构、浓度因素和溶剂效应的考察发现,三者对囊泡的形成都具有明显的影响,这与实验方面得到的结论基本符合。第五章考察A₃B₁嵌段共聚物对疏水纳米颗粒聚集行为的调控作用。当疏水纳米颗粒单独存在于溶剂中时,它们会聚集成一个致密的团簇。当嵌段共聚物与纳米颗粒共同存在于溶剂中时,由于纳米颗粒的疏水性、A₃B₁链的两亲性及纳米颗粒与A链段的相互吸引作用,最终纳米颗粒均分布在A₃B₁的囊泡壁中。对于性能不同的两种混合纳米颗粒,通过与A、B链段的选择性相互作用,实现一种纳米颗粒位于囊泡核,另一种纳米颗粒位于囊泡壁。在除去A₃B₁嵌段共聚物后,我们就可以得到单一纳米颗粒的空心球结构和核-壳结构的复合材料。第六章为全文总结及展望。更多还原

【Abstract】 Recently, various efforts have been made to synthesize inorganic materials with controlled size or morphology, because of their potential applications in various fields such as catalysis, medicine, dye, and cosmetic. A large amount of experiments have found that block copolymers exert strong effect on the nucleation, the growth of crystal, and subsequently affect the morphology of crystal. However, the mechanism of the block copolymer controlled or directed crystal growth is still not clear. Computer simulations can provide fundamental insight into crystallization process directed by polymer and knowledge on important parameters governing the fabrication of inorganic particles with complex structures. So far, however, rare such computer simulation efforts have been reported.In this thesis, the formation mechanism of diblock copolymer vesicle was investigated using bond-fluctuation dynamic Monte Carlo method based on simple cubic lattice. The influence of the chain concentration, chain structure and the solvent property on the vesicle size was discussed. The solvent property was found to affect the vesicle formation process. At last, the directed loading of nanoparticles and mixed nanoparticles in vesicle was studied in detail.Chapter 1 introduced the experimental reports and computer simulation results on the self-assembly of block copolymers in solution.Chapter 2 introduced the principle of Monte Carlo method and its application in polymer science. The model used in this thesis was also elucidated.In chapter 3, the formation mechanism of amphiphilic diblock copolymer vecisle was investigated in detail. AmBn represents the amphiphilic diblock copolymer chain with hydrophobic A segments and hydrophilic B segments. Pairwise nearest-neighbor (NN) interactions and next nearest-neighbor (NNN) interactions are considered among chain segments A, B and solvent segment S. The amphiphilic property of A3B1 chain is represented by the attractionεAA = -1 between NN or NNN A-A beads. While the interaction parameterεBB andεABwere assumed to be zero for A-A and A-B interactions. For A3B1 chains, a single vesicle was obtained when the segment concentration of polymer chain Cp = 7%. A segments were found to locate in the wall of vesicle, while B segments concentrated at its interior and exterior surfaces. The formation process of vesicle was investigated in detail, a bilayer disk was aggregated in a randomly dispersed system, it then bended and encapsulated solvents, and finally closed up to form a vesicle. The formation mechanism of vesicle agreed with the previous reports of MD, BD, DPD, and density functional simulations. However, the bending of the bilayer disk was observed for the first time by using a lattice chain model.The influence of the chain concentration, chain structure and the solvent property on the vesicle size was investigated in chapter 4. Vesicular structure could be formed when m≥3 with n = 1. The vesicle size increased with the segment concentration when the segment concentration of A3B1 chains was in the range of 2% and 15%. The solvent property, which was represented by the repulsive interactionεBS between bead B and solvent, was found to affect the vesicle formation process. For a smallεBS < 0.05, the vesicle formation pathway was the same as that discovered in chapter 3. While forεBS≥0.05, the vesicle was formed through another mechanism: The randomly distributed chains quickly assembled into spherical aggregates, which further grew through the coalescence of aggregates or the evaporation-condensation-like process. When the spherical aggregate size reached an enough big value, A segments and solvents entered into the center of the sphere, resulting in the formation of vesicle. We also found that the vesicle size decreased with the increase ofεBS. That means we can control the vesicle size by adjusting the solvent property.Chapter 5 investigated the aggregation of nanoparticles in the presence of diblock copolymer. Due to the hydrophobic property, nanoparticles intended to form a big and compact aggregate in absence of block copolymer. The aggregate behavior of nanoparticles changed once upon addition of A3B1 diblock copolymers, where an additional attractive interaction between nanoparticles and A segment was introduced. It was observed that nanoparticles dispersed in the wall of vesicle. It is easy to image that a hollow sphere will be fabricated by nanoparticles after the calcination of copolymers. The loading of mixed nanoparticles in vesicle was also studied. We introduced an attraction between nanoparticle I and A segment, and a smaller attraction between nanoparticle II and B segment. After a long time movement, we found that nanoparticle I located in the vesicle wall, and nanoparticle II was loaded into the core of vesicle. Therefore, we will obtain the core-shell structure of mixed nanoparticles after the calcination of copolymer. The simulation demonstrates that addition of block copolymer can effectively control the aggregation of inorganic particles and lead to formation of a variety of nanostructures.更多还原