两端接枝聚合物的金纳米棒在乳液液滴中的受限组装

Confined assembly of gold nanorods with end-grafted polymers in emulsion droplets

聚合物接枝金纳米棒(polymer grafted gold nanorods, AuNRs@Polymer)不仅具有聚合物的稳定性、功能性和可设计性,还具有金纳米粒子(gold nanoparticles, AuNPs)的光学、光热转换、等离子体等性质,在成像、光电器件和药物控释等领域具有重要的应用前景.两端接枝聚合物的金纳米棒(AuNRs@End-Polymer)由于聚合物选择性接枝在金纳米棒的两端,易形成软硬兼具的哑铃状纳米粒子(类似ABA型嵌段共聚物).哑铃状纳米粒子受其两端特殊的空间位阻影响,在受限空间中难以形成紧密稳定的肩并肩结构,而更倾向于形成倾斜、交叉或螺旋排列等新颖结构.本文系统地研究了三维受限空间的尺寸以及纳米粒子形貌等因素对AuNRs空间排布的影响,并构建了一系列有序组装结构.

Polymer grafted gold nanorods(AuNRs@Polymer) combine the stability, functionality and designability of polymers, as well as the functional properties of gold nanorods(AuNRs). Compared with a single AuNR, the ordered assemblies of AuNRs@Polymer generally show more extraordinary physical and chemical properties, including antibacterial materials,photothermal conversion, surface enhanced Raman scattering, and others. In recent years, numerous assembly methods including ligands-directed assembly, external filed assisted assembly, template-assisted assembly and selective solvent method etc. were used to fabricate ordered arrays of AuNRs. Among them, confined assembly is one of the effective methods for the preparation of the ordered assemblies.In confined space, the morphology of nanoparticles(NPs) plays an important role in the assembly process. Compared with spherical NPs, AuNRs@Polymer possess anisotropic morphologies and are expected to show rich assembly behaviors in confined space. However, the high energy barrier caused by the anisotropic morphology of AuNRs generally leads to disordered orientation and polydispersed assembly morphology. Besides, AuNRs with end-grafted polymer(AuNRs@End-Polymer) have more complex structures and can form special dumbbell shapes(similar to ABA block copolymer)with soft ends and hard core. Due to the steric hindrance at both ends of the dumbbell shaped NPs, it is more difficult to obtain the ordered structure of AuNRs@End-Polymer in a confined space, compared to the AuNRs with polymer grafted on the whole surface(AuNRs@Full-Polymer).This work reports a facile way to fabricate ordered assemblies of AuNRs@End-Polymer from three-dimensional(3D)confined assembly. A 3D soft confined space provided by emulsion droplets was used to study the assembly behavior of AuNRs@End-Polymer in confined space. By using the 3D confined assembly method, a series of ordered assemblies with different AuNRs were fabricated. The effects of the AuNRs morphology and the size of confined space on the microstructure of assemblies were systematically studied as well.Our experimental results prove that AuNR@End-Polymer can form dumbbell-shaped morphology. It has been observed that the dumbbell-shaped AuNRs prefer to pack into stagger, spiral or cross arranged morphology, whereas the rod-shaped AuNRs@Full-PS prefer to pack side-by-side. In addition, when the volume of gold core is relatively large, the AuNRs perform like rigid rod and it is easier to form an ordered assembly in the confined space. When the volume of polymer ligands is relatively large, the polymer plays a leading role in the assembly process and prefers to result in the relatively chaotic arrangement of AuNRs. These results demonstrate that the arrangement of AuNRs depends on the morphology of the NPs in the confined space. By designing gold NPs with different morphologies, it is expected to obtain ordered assemblies with different arrangements. This provides a new idea for the self-assembly of AuNRs to form ordered structures which show a great potential application prospect in many fields.