嵌段共聚物自组装形成各向异性纳米粒子的模拟研究

In recent years, anisotropic nanoparticles, such as patchy, multi-compartment and Janus particles have attracted tremendous scientific interests due to their novel morphologies and potential application in fabrication photonic crystals, target drug delivery, bionic self-healing materials, electronics, biological and optical sensor, antireflection coatings and anisotropic building blocks for complex structures. Block copolymers have the most fascinating characteristic of most soft matter, that is, they can form rich and controllable variety of microstructures at nanoscale via self-assembly which made them be a suitable and promising candidate for fabricating anisotropic morphologies. In this project, we will systematically investigate the self-assembly behavior of block copolymers in solvent and under various confined states using simulated annealing technique. The research priorities are predicting novel morphologies, especially, searching the requirement of forming anisotropic morphologies and elucidating the underlying physical rules. On one hand, in solution, we systematically study the influence of the polymerization, volume fraction, concentration of the block copolymers and the selectivity of solvent, on the self-assembled morphologies. On the other hand, based on the idea of confinement inducing broken of symmetry of a structure, we systematically study the influence of confinement effects, including surface-polymer interactions and the degree of structural frustration with different pore size and shape, on the self-assembled microstructures. We will elucidate the origin of the anisotropic morphologies and the mechanism for the morphological transitions between different morphologies base on the analysis and calculation of systematic information such as chain conformation with mean-square end-to-end distance, specific heat, average-contact number et al. and free energy. Furthermore, besides predicting equilibrium morphologies using simulated annealing technique, we are going to apply Lattice Boltzmann Method on the dynamical study of aforesaid polymer system. We hope our study can provide deeply understand of the phase behavior and guidelines for obtaining the predicted structures experimentally.

各向异性纳米粒子新奇的结构和其在仿生材料制备、药物携带与释放、电子工程、光子晶体等多个学科领域的应用前景，得到了科研人员的广泛关注。在其制备方法中，嵌段共聚物由于能够自组装形成丰富的纳米尺度结构以及这些微相结构易于调控性，成为目前最有效和最有前景的方法之一。所以，本项目采用模拟退火方法研究嵌段共聚物自组装形成各向异性结构的条件以及物理机理。研究体系为共聚物溶液和空间受限体系。主要考察溶液体系中共聚物浓度、链长、体积分数、溶液选择性等对自组装形态的影响；利用受限产生对称性破缺这一思想，构建不同的受限环境以考察其对自组装形态的影响；基于共聚物链物理量的统计以及自由能的计算，揭示各向异性结构形成原因和不同形态之间的转变路径及其物理机理；在正确预测平衡态结构的基础上，利用格点玻尔兹曼方法探索其动力学行为，从而全面加强对这类特殊结构相行为的认识和理解，为新型功能材料的设计和应用提供理论指导和依据。

制备高度有序和结构可控的纳米材料一直是现代材料科学和纳米技术中的关键问题。在本项目中，我们首先系统地研究了体相为层状结构的双嵌段共聚物受限在三角形、正方形以及椭圆形纳米孔道时自组装形态。研究结果表明，受限孔道的几何形状以及表面性质对自组装结构和层状结构的取向有很强的影响。当受限孔道表面性质为中性时，始终形成层状垂直层结构。当孔道表面作用有选择性时，自组装结构依赖于受限孔道的形状、大小和表面选择性强弱等因素。通过进一步的数据分析发现这些得到的自组装结构是由于体系中界面能、表面能和熵的相互竞争产生的结果。研究结果为获得新结构调控层状纳米结构在材料中的取向等问题提供了理论依据。其次，我们系统地研究了线型三嵌段共聚物受限在球形纳米孔内的自组装形态。研究表明，当孔壁吸引两端嵌段时，共聚物自组装形成多种各向异性纳米粒子。在小孔径下随着球状纳米孔孔径的增加，依次观察到补丁数为1，2，4，5，6，7的补丁状各向异性纳米结构。当改变孔壁和两端嵌段作用力强度时，自组装形态发生了改变，我们观察到了一系列的结构转变并通过体系中物理量的分析将其原因归结为系统熵的效应。另外，我们发现自组装形态主要由中间B嵌段的组分大小所决定，而内部结构主要由两端嵌段体积分数的比值所决定。结果表明研究中得到的各向异性纳米材料性质可以通过控制孔径、作用力和共聚物组分来进行调控。研究结果提供了制备一类“智能纳米粒子”的途径，其在仿生材料、药物输运等领域有着广泛的应用前景。另外，我们参与了研究可控制备石墨烯、生长机理探讨以及场发射性能优化。研究表明石墨烯的形貌由生长时间、碳源气浓度、微波功率等因素强烈影响。通过和一系列实验对比定性分析了石墨烯可能的生长机理。发现石墨烯在碳纳米管上稀疏分布时，复合材料能在保证碳纳米管大长径比的基础上，使石墨烯的锋锐边缘成为有效的场发射点，从而使复合材料的场发射性能相比于原始碳纳米管阵列有了大幅度的提升。