【作者】 李帆；

【导师】 张连斌； 熊必金；

【作者基本信息】 华中科技大学 ， 高分子化学与物理， 2021， 博士

【摘要】 聚合物接枝金纳米粒子(AuNPs@polymer)兼具聚合物的稳定性、功能性和可设计性,以及金纳米粒子(AuNPs)的光、热和催化等特性。此外,AuNPs@polymer还可以通过自组装来构建结构和功能丰富的有序纳米复合材料,在催化、成像、光电器件和药物控释等领域具有重要的应用前景。AuNPs在复合材料中的空间有序排列不仅依赖于金核的分散性和尺寸等参数,也取决于表面聚合物配体的物化性质和接枝区域。因此,将不同聚合物有选择性地修饰在AuNPs表面的不同区域,对于新型AuNPs@polymer及其有序组装体的制备具有重要意义。然而,克服AuNPs表面的对称性,构建区域性异质结构十分困难,导致目前区域选择性AuNPs@polymer的制备方法普遍存在过程复杂、重复性差,接枝密度较低等问题。本论文发展了两种AuNPs的区域选择性修饰方法,将聚合物配体定向修饰在AuNPs表面选定的区域,制备了一系列区域选择性AuNPs@polymer。这类AuNPs被赋予了可控的表面异质结构,同时还具备类似嵌段共聚物的组装行为。利用模板诱导法、选择性溶剂法和受限组装法,本论文系统性地研究了区域选择性AuNPs@polymer的微观结构对其空间排列方式的影响,阐明了金核及表面聚合物配体在自组装过程中的作用机制,实现了AuNPs@polymer的定向、分级自组装,并构建了多种AuNPs有序组装体。具体研究内容如下:(1)发展了“等离子体刻蚀-配体接枝”法,实现了金纳米球的区域选择性修饰。利用等离子体刻蚀掉AuNPs单层膜上表面的配体,再通过配体交换法在AuNPs裸露的上表面接枝另一种聚合物配体,制备了两个半球修饰不同聚合物的Janus(AB)型AuNPs。该方法适用于多种聚合物配体,具有普适性。此外,还可以通过控制等离子体刻蚀的功率,实现金纳米球表面二元配体比例的精确控制。该方法得到的Janus纳米粒子具有类似两嵌段共聚物的性质,可通过模板诱导法实现定向组装,也可用于基板的亲疏水改性及稳定油/水乳液。(2)发展了“溶剂溶解性介导”法,实现了金纳米棒(AuNRs)的区域选择性修饰。利用AuNRs侧壁在不良溶剂中难以实现配体交换的特点,选择性地将聚合物接枝在AuNRs的两端,制备了ABA型AuNRs。进一步利用良溶剂在侧壁接枝另一种聚合物制备了结构和性能更为复杂的二元聚合物修饰的ABA型AuNRs。探讨了AuNRs的表面配体修饰机理并研究了溶剂溶解性对聚合物接枝区域的影响。同时,通过生长二氧化硅壳层、银壳层和络合量子点等方法确定了聚合物的接枝区域,证明了该方法的有效性和普适性。(3)研究了二元聚合物修饰的ABA型AuNRs在选择性溶剂中的组装行为。在选择性溶剂中,利用溶剂对AuNRs两端和侧壁两种配体的不同溶解性实现了AuNRs的定向组装。通过控制混合溶液的组分,实现了AuNRs的分级组装。阐明了AuNRs不同区域的配体对其组装行为的影响,明确了不良溶剂驱动纳米粒子分级组装的过程。以二元聚合物修饰的ABA型AuNRs为组装基元,模拟了ABA三嵌段共聚物的组装行为,证明了该纳米粒子具备类似嵌段共聚物的性质。(4)研究了ABA型AuNRs的形貌及其在受限空间中的组装行为。两端的聚合物配体在组装过程中极易塌缩,反向折叠包覆在两端,形成软硬兼具的哑铃状纳米粒子。哑铃状纳米粒子受其两端特殊的空间位阻影响,在受限空间中无法形成紧密稳定的肩并肩结构,更倾向于形成倾斜、错排或螺旋排列等特殊结构。系统地研究了受限空间的维度、尺寸以及纳米粒子形貌对AuNRs空间排布的影响,并构建了一系列一维、二维和三维有序组装结构。更多还原

【Abstract】 Polymer-grafted gold nanoparticles(AuNPs@polymer)combine the stability,functionality and designability of polymers,as well as the optical,thermal and catalytic properties of AuNPs.In addition,AuNPs@polymer can also construct ordered nanocomposites with rich structures and functions through self-assembly.These ordered nanocomposites have important potential applications in catalysis,imaging,optoelectronic devices and drug delivery fields.The ordered arrangement of AuNPs@polymer in the composites not only depends on the dispersion and size of the gold core,but also on the physicochemical properties and grafting region of surface polymer ligands.Therefore,selective modification of different polymers on different regions of AuNPs is of great significance for the preparation of novel AuNPs@polymer and its ordered assemblies.However,it is very difficult to overcome the symmetrical structure of the surface of the AuNPs and construct regional heterogeneous structures,resulting in problems in the preparation of regioselective AuNPs@polymer,such as complex process,poor repeatability and low grafting density.In this thesis,two regioselective modification methods of AuNPs were developed.Polymer ligands were directionally modified in the selected region of the surface of AuNPs,and a series of regioselective AuNPs@polymer were prepared.These AuNPs are endowed with regional heterostructures and exhibit abundant assembly behaviors similar to block copolymers.Using the template induction method,selective solvent method and confined assembly method,this thesis systematically studied the effect of the microstructure of regioselective AuNPs@polymer on their spatial arrangements,clarified the mechanism of gold core and surface polymer ligands in the assembly process,realized the directional and hierarchical self-assembly of AuNPs@polymer,and constructed a variety of AuNPs ordered structures.1)The “plasma etching-ligand grafting” method was developed to realize the regioselective modification of gold nanospheres.The ligands on the upper surface of AuNPs monolayer were etched by plasma,and then another polymer ligands were grafted on the exposed upper surface of AuNPs by ligand exchange method.Janus(AB)type AuNPs with different polymers modified on upper and lower hemispheres were prepared.This method can be applied to a variety of polymer ligands,and can be used to accurately control the ratio of binary ligands on the surface of gold nanospheres by controlling the power of plasma etching.The obtained Janus NPs can be used to simulate directional assembly of diblock copolymers by template induction method,and can also be used for the hydrophilic and hydrophobic modification of the substrate and the stabilization of oil/water emulsions.2)The “solvent solubility mediated” method was developed to realize regioselective modification of gold nanorods(AuNRs).Taking advantage that the side of the AuNRs are difficult to achieve ligand exchange in poor solvents,selectively grafting polymers at both ends of AuNRs,ABA type AuNRs were prepared.Furthermore,binary polymers modified ABA type AuNRs with more complex structure and properties were prepared by grafting another polymer on the side in the second step.The mechanism of surface ligands modification of AuNRs was discussed,and the effect of solvent solubility on the grafting region of polymer was deeply studied.The grafting region of the polymers,the effectiveness and generality of this method were proved by growing silica shell,silver shell and complexing quantum dots.3)The assembly behavior of binary polymers modified ABA type AuNRs in selective solvents was investigated.In selective solvents,the different solubility of the two ligands on the surface of AuNRs was used to realize the directional assembly of AuNRs.By controlling the composition of the mixed solution,the hierarchical assembly of AuNRs was realized.The effects of ligands in different regions of AuNRs on the assembly behavior were clarified,the hierarchical assembly process of NPs driven by poor solvents was cleared.The assembly behavior of ABA triblock copolymer was simulated by using binary polymers modified ABA AuNRs as assembly unit.It was proved that these NPs have similar properties to the block copolymer.4)The morphological characteristics of ABA type AuNRs and their assembly behavior in confined space were studied.The polymer ligands at ends are prone to collapse during the assembly process,forming a dumbbell-shaped NPs with both soft and hard regions.Affected by the special steric hindrance at both ends,the dumbbell-shaped NPs are unable to form a tight and stable side-by-side structure in the confined space.They are more inclined to form special structures such as tilt,stagger or spiral arrangement to maintain the stability of the assembly.The effects of dimension,size and morphology on the spatial arrangement of AuNRs were systematically studied,and a series of ordered one-dimensional,two-dimensional and three-dimensional structures were constructed.更多还原