Surface Modification And Self-Assembly Of Titanate Nanotubes

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.