【作者】 高嫄；

【导师】 颜德岳； 周永丰；

【作者基本信息】 上海交通大学 ， 材料学， 2009， 博士

【摘要】 出于对提高一维纳米材料的溶剂溶解性和利用其优异性能来制备功能纳米材料及器件的强烈需要,最近数年来,一维无机、有机纳米材料例如碳纳米管(CNT)等的功能化或表面修饰吸引了人们越来越多的关注,尤其是在其表面进行分子设计,更是广受科学界的关注。因而,用大分子价键修饰纳米管是制备可溶性无机纳米管的一个重要方法,由于高分子长链有助于纳米管在许多溶剂中溶解,即使较低程度的改性。目前“接上去”和“接出来”这两种方法得以发展起来,实现了将聚合物共价接枝到固体基底的表面。前者是直接将特定大分子末端所含有活性官能团(例如-OH等)与一维纳米材料表面存在或预先处理所得到活泼官能团直接反应得到的。这种方法操作简单,但是存在接枝后聚合物链的热和溶剂稳定性差、接枝密度低、接枝厚度不可控等缺点。因为人们的注意已经转移到“接出来”这种方式,可以通过在纳米材料基底的外表面直接用商业化的那些聚合单体来生长大分子。不过在一维纳米材料大分子功能化领域依然存在很多问题,例如:(1)大分子接枝质量的可控性;(2)所接枝大分子结构和性能的设计;(3)制备基于纳米管状材料的智能纳米材料(或称为分子器件)。本论文的工作是基于上述发展趋势以及研究背景展开的。利用活性/可控原子转移自由基聚合(ATRP)这一构筑聚合物材料的强有力工具和非共价接枝改性的方法,本文对钛酸纳米管功能化“接出来“方式进行了推进,在钛酸纳米管(TNT)表面实现了一系列丙烯酸类、苯乙烯类和丙烯酰胺类ATRP活性聚合单体的原位聚合和共聚反应。基于原位ATRP“接出来”方式,解决了(1)大分子的接枝量可以通过调节单体和钛酸纳米管引发剂(TNTs-Br)的加料比得到很好控制;(2)通过分子设计,使两嵌段大分子接枝到了钛酸纳米管;(3)获得了智能型温度和pH敏感的钛酸纳米管/聚合物复合纳米材料。具体开展了以下几方面的研究工作:1.制备聚甲基丙烯酸甲酯功能化的钛酸纳米管通过“接出来”方式,应用原位ATRP (原子转移自由基聚合)法,成功将聚甲基丙烯酸甲酯(PMMA)接枝到钛酸纳米管的外表面。聚合物的厚度通过单体与引发剂TNTs-Br的相对加料量来控制。所得到的基于钛酸纳米管纳米复合材料用FTIR、1H NMR、SEM、TEM和TGA进行了表征。同时,这一方法延展到了共聚体系获得两嵌段聚合物功能化的钛酸纳米管(PMMA-b- PHEMA-g- TNTs)。这种方法为制备新颖的、具有设计的化学结构、基于钛酸纳米管的纳米材料、纳米结构和纳米器械等开辟了一条道路。2.钛酸纳米管的聚苯乙烯功能化将由TNTs-Br引发原位ATRP聚合的新策略扩展到苯乙烯单体,在Cu(I)Br/N, N, N′, N",N"-五甲基二乙基三胺(PMDETA)催化下,100oC下,TNTs-Br引发苯乙烯单体聚合得到了聚苯乙烯(PS)接枝的钛酸纳米管PS-g-TNTs。PS的分子量和聚合物层的厚度都得到控制。样品的TEM图表明形成了以钛酸纳米管为核,聚合物为壳的核-壳型纳米结构。FTIR, 1H NMR, SEM及TGA用来表征此纳米材料的化学结构等。为了进一步讨论钛酸纳米管和PS之间的共价连接,对所得的PS修饰钛酸纳米管进行了化学降解和热降解来剥落PS层。对PS-g-TNTs和剥掉PS的钛酸纳米管基于TEM和SEM的对比研究更加清楚的表明了共价接枝这一特点。这为钛酸纳米管表面ATRP的应用进一步铺平了道路。3.特殊功能性聚合物对钛酸纳米管的功能化在钛酸纳米管表面引发单体N-异丙基丙烯酰胺的原位聚合,得到温敏水溶性聚合物功能化的钛酸纳米管。FTIR、1H NMR、TEM、SEM、TGA、AFM等手段证明了聚N-异丙基丙烯酰胺修饰钛酸纳米管的结构及形貌,变温UV-vis和1H NMR谱说明产物具有良好的温度敏感性。引发单体甲基丙烯酸-2- (N,N-二乙氨基)乙酯的聚合,得到pH敏感水溶性聚合物接枝的钛酸纳米管纳米管。4.聚赖氨酸与钛酸纳米管有机/无机纳米杂化材料的制备通过静电作用力,成功制备了聚赖氨酸/钛酸纳米管有机/无机纳米杂化材料。研究发现,在酸性环境中,聚赖氨酸/钛酸纳米管有机/无机纳米杂化材料具有良好的水溶性;在碱性环境中聚赖氨酸/钛酸纳米管有机/无机纳米杂化材料从水中沉淀出来,同时我们也发现,在纳米管表面得到的聚赖氨酸的纳米结构也发生变化。低溶液pH值时,聚赖氨酸以“珠穿线”方式缠绕到钛酸纳米管上;高溶液pH值时,聚赖氨酸包覆到钛酸纳米管表面形成聚合物层。不同形状的聚赖氨酸纳米结构有可能作为模板来定位吸附其它有意义的生物分子,有望用于生物或化学传感器排列,为研制功能化纳米器件提供了可能。5.直链淀粉/钛酸纳米管复合物的分级自组装行为研究单个纳米材料例如纳米颗粒、纳米管和纳米棒等的分级自组装是通过自底而上方法构建复合超分子体系的仿生技术,最近越来越引起人们的关注。本章通过一种新技术实现了尺寸和结构复杂化可控性高的单根纳米管的分级自组装。直径是10nm左右的纯钛酸纳米管被直链淀粉在表面缠绕进行改性,功能化的钛酸纳米管进而自组装形成直径约100-500nm的纤维束,相邻的纳米管之间的直链淀粉与直链淀粉之间的相互作用使单根纳米管沿着纤维束的轴线排列。有趣的是,纤维束进一步促进未反应的直链淀粉组装形成微米尺寸的、梭状六方体单晶,高度取向的钛酸纳米管为核,外层是直链淀粉的壳。如此结构的分级自组装体系可以通过改变钛酸纳米管和直链淀粉的浓度而分别改变。这项工作开创了一种简单的自底而上、制造有序的从一维到三维的杂化体材料的路线。6.一维棒状病毒体----烟草花叶病毒在多肽调控下的组装通过静电相互作用,成功制备了一种新型的聚赖氨酸/烟草花叶病毒(TMV)有机/无机杂化纳米管,并实现了pH调控下纳米管的多维、多尺度组装。研究表明,在中性和酸性环境下,TMV在聚赖氨酸作用下趋向以“肩并肩”方式组装,形成一维的纳米纤维和两维的结构;在碱性环境下,TMV以“头-尾”方式连接成Y型接头,并进一步组装形成三维的网络结构。另外,我们还发现了聚赖氨酸在TMV作用下的特殊构象转变,包裹在纳米管表面的聚赖氨酸在从酸性到碱性的整个pH范围内都会采取螺旋构象,这和其在溶液中的构象转变是完全不同的。这种环境响应的复合组装体在纳米电子元件、纳米感应器、药物基因传输系统有着广泛的潜在应用。更多还原

【Abstract】 Functionalization and regulation of one-dimensional nanomaterials, such as titanate nanotube (TNT) has aroused increasing interest due to the strong desire to improve inorganic nanomaterials’solubility and the fascinating capacity to fabricate novel nanomaterials and nanodevices by molecular design and tailoring. The modification of nanotubes via anchoring macromolecules onto the surface is most favorite method to improve the solubility in organic solvents. Thus, the“grafting to”and“grafting from”approaches were developed in order to bond polymers to nanotubes. The former involves direct reaction of existing polymers containing terminal functional groups (e.g., OH) with the anterior functional groups (e.g., -OH) on TNTs. The apparent limitation of the“grafting to”approach lies in; (1) the specific requirement of the polymer terminal functional groups, (2) the low grafting density, and (3) limited control over the grafted polymer quantity. Therefore, the attention has shifted to the grafting from approach, which makes direct growth of general polymers on the sidewalls of TNTs from commercially available monomers possible. Up to now, three main challenges still span the macromolecule-functionalization area of TNTs: (1) the controllability of the grafted quantity; (2) design and tailoring of structure and property for the coupled macromolecules; and (3) fabrication of TNTs-based smart nanocomposites (or molecular devices). This thesis will attempt to meet the challenges, and then to unlock the new interpenetrating area of chemistry, materials, physics, and TNTs.Taking advantage of the merits of living/controlled atom transfer radical polymerization (ATRP), a very powerful tool for building of polymeric materials, the thesis of this dissertation advanced the grafting from approach, and realized a series of in situ polymerization and copolymerization of acrylate-, styrene-, and acrylamide-type ATRP-active monomers on the surfaces of titanate nanotubes. Depending on the presented in situ ATRP“grafting from”approach, three big problems aforementioned were basically resolved: (1) the grafted polymer quantity can be well controlled by the feed ratio of monomer/TNTs-supported initiators (TNTs-Br); (2) amphiphilic polymer layers were coated on TNTs surfaces by molecular design and tailoring; and (3) smart thermal- and pH- sensitive TNTs-polymer nanohybrids were successfully prepared.The details are as follows:1. Preparation of PMMA grafted TNTsIn situ ATRP“grafting from”approach was successfully applied to graft poly (methyl methacrylate) (PMMA) onto the surfaces of TNTs. The thickness of the coated polymer layers can be conveniently controlled by the feed ratio of MMA/TNTs-Br. The resulting TNTs-based polymer brushes were characterized and confirmed with FTIR, 1H NMR, SEM, TEM and TGA. Moreover, the approach has been extended to copolymerization system, affording novel hybrid core-shell nanoobjects with TNTs as the core and amphiphilic poly (methyl methacrylate)-block-poly (hydroxyethyl methacrylate) (PMMA-b-PHEMA) as the shell. The approach presented here may open an avenue for exploring and preparing novel TNTs-based nanomaterials and molecular devices with tailor-made structure, architecture and properties.2. Functionalization of TNTs with polystyrene and defunctionalization of the productsA core-shell hybrid nanostructure, possessing a hard backbone of TNT and a soft shell of brush-like polystyrene (PS), was successfully prepared by in situ ATRP, using Cu(I)Br/N,N,N’,N”,N”- pentamethyldiethylenetriamine (PMDETA) as the catalyst, at 100oC in diphenyl ether solution. The molecular weight of PS was well controlled, as was the thickness of the shell layer. TEM images of the samples provided direct evidence for the formation of a core-shell structure, i.e., the TNTs coated with polymer layer. FTIR, 1H NMR, SEM and TGA were used to determine the chemical structure, morphology and the grafted PS quantities of the resulting products. In order to further establish the covalent linkage between PS and nanotubes moieties, the resulting PS-functionalized TNTs were defunctionalized by hydrolysis decomposition. Comparative studies, based on TEM images between the PS-functionalized and chemically defunctionalized TNTs samples revealed the covalent coating character. Further copolymerization of tert-butyl acrylate (tBA) with the PS-linked TNTs as initiators was realized, illustrating that the PS species is still“living”although the lower controllability of PDI. It is expected that achieving these hybrid objectives, on the basis of such simple grafting, will pave the way for the design, fabrication, optimization, and eventual application of more functional TNTs-related nanomaterials.3. Smart thermal and pH- sensitive and photoluminecent TNTsThermo-responsive titanate nanotubes (PNIPAAm-g-TNTs) were successfully prepared by in situ ATRP, and the chemical structure and morphology were determined using FTIR, 1H NMR, SEM, TEM, TGA and AFM. Temperature-variable UV-vis and 1H NMR and repeated DSC proved that the product had good thermo-responsive property and perfect reversibility.The pH-sensitive property of titanate nanotubes hybrids were also obtained by the surface-initiated ATRP process by fabricating PDEAEMA-g-TNTs.4. The preparation of polylysine/TNTs hybrid nanomaterialsWe present novel intelligent polylysine/titanate (PLL/TNTs) nanotubes hybrid nanomaterials, in which the complexation of anionic TNTs and cationic PLL through electrostatic interactions between them can be manipulated by pH value. In addition, the topology of PLL coated on TNTs changed with changing of the solution pH. Below the isoelectric point (pI) of PLL, it is positive charged and adopts random coil conformation. Under this situation, the PLL is found to adsorb onto TNTs with“bead-on-string”binding topology. Higher than pI, the PLL is negative charged and adoptsα-helix conformation, which makes PLL immobilize on surfaces of TNTs to form a polymer layer. We also explored what driving force can induce the pH-responsive solubility of PLL/TNTs in aqueous medium.5. Hierarchical self-assembly of individual amylose/titanate nanotubesHierarchical self-assembly of individual nanostructures such as nanoparticles, nanorods and nanotubes, is a bioinspired technology to construct complex supramolecular architectures through a bottom-up approach, and has received more and more attention in recent year. Herein, we reported a novel strategy to realize the hierarchical self-assembly of individual nanotubes with a high controllability in dimension and structure complexity. Pristine TNTs around 10nm were first helically wrapped with amylose on the surface, and then the functional TNTs were self-assembled into fibers around 100-500nm in diameter with the nanotubes aligned along the fiber axis through amylose-amylose interactions between adjacent nanotubes. Interestingly, the fibers will further organize the free amylose to self-assemble into micrometer-sized shuttle-like hexagonal single crystal with an inner highly orientated TNTs core and outer amylose shell. Such a hierarchical self-assembly was achieved solely by changing the concentration of the TNTs and amylose. The finding opens a simple bottom-up route for fabrication of ordered hybrid materials from one dimension (1D) to three dimensions (3D).6. Nanobiocomposite Fibers by Controlled Assembly of Rod-like Tobacco Mosaic VirusOne-dimensional composite materials were generated by electrostatic interaction between tobacco mosaic virus (TMV) and biomacromolecule. These composite have the head-to-tail and network assembly of TMV. Two factors contribute to the formation of such TMV-composite materials: (1) the accumulation and electrostatic interaction on the surface of TMV; and (2) the possibility of prolongation and stabilization of TMV helices. Because of polylysine are tailored to the exterior surface of TMV, electrostatic interaction can induce TMV to form branched structures with knot-like connections. Further, concentration and pH value of solution can munipulate the assembly morphology of TMV. TEM and SEM are used to analyze the morphology and structure of composite. This strategy to assembly TMV into 1D supramolecular assembly could be utilized in the fabrication of advanced nanomaterials based on virus for potential applications including electronics, optics, sensing, and biomedical engineering.更多还原