• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2
  • 1
  • Tagged with
  • 3
  • 3
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Selective Interfacial Interaction between Diblock Copolymers and Cobalt Nanoparticles

David, Kasi 20 November 2006 (has links)
In order to optimize the synthesis of metal nanoparticle-polymer systems, there are certain processes which must be understood. Perhaps the most important one is the selective interfacial interaction between the block copolymer and the growing metal nanoparticles. To investigate this interaction, four different approaches were taken. The first approach looked at the strength of interaction between the competing blocks of the copolymer and the metal nanoparticles surface. The second approach looked at the effect of polymer architecture on the metal nanoclusters. The third approach looked at the polymer composition and solvent effects on the phase behavior of the metal nanocluster-block copolymer nanocomposite. Finally, the influence of the metal precursor on the rate of the decomposition was examined. It was found that adsorbed layers of PS on the cobalt nanoparticles are completely displaced by PMMA when the solvent is a common good solvent. An adsorbed layer of only PMMA is also obtained through competitive adsorption from a common good solvent. However, in a selective solvent that is poor for PS, sequential adsorption leads to the formation of mixed layers. In homopolymer solutions, the cluster size reaches a minimum at a finite chain MW. In the case of diblock copolymers, the only parameter (for a fixed copolymer concentration) controlling the cluster size in suspensions of di-block copolymers is the molecular weight of one block, in this case PMMA, and is indifferent to other parameters including the molecular weight of the other block (PS) or the solvent quality. It was also found that the spatial distribution of the metal clusters synthesized in-situ coincided with the morphology dictated by thermodynamically-driven microdomain structure of the block copolymer. Moreover, the overall final morphology of the nanocomposite is locked into place while in solution, and fast solvent evaporation does not cause this morphology to change. Finally, results showed that the rate of nanocomposite synthesis occurred faster in the PS suspensions compared to PMMA, indicating that chemical bonds between PMMA and the cobalt nanoclusters slowed the thermal decomposition of the metal precursor. So the PMMA chains provided sites for nucleation, but did not necessarily aid particle growth.
2

Metal

Karakoc, Nihan 01 February 2009 (has links) (PDF)
This study aims synthesis of metal/polymer one dimensional nanostructures by micelle formation, reduction, and electrospinning route, and to analyze the morphological characteristics of composite nanofibers. The study was carried out in three main steps. First, the reverse micelle structures were established between the anionic surfactant and the metal ion. The surfactant acts as an agent to bind metal ions together so that the arrangements of metal ions can be controlled in the solution. As the surfactant concentration increases, reverse micelles grow and reverse wormlike micelle structures are observed. Wormlike micelles are elongated semi flexible aggregates which form a spherocylinder form repeating units. Metal ions are in the core and surrounded with the surfactant. The polymer attached to the wormlike structure acts as a shield and prevents phase separation in a hydrophilic medium. Different polymer and surfactant concentrations were tried to determine the optimum polymer and surfactant concentrations for reverse micelle formation. The size analyses of the reverse micelle structures were done by dynamic light scattering technique. In the second step, metal ions in the micelles were reduced by using hydrazine hydrate to obtain metal cores in the center of wormlike micelles. Finally, electrospinning was carried at room temperature and in air atmosphere. The characterization of nano composites was done by Scanning Electron Microscopy. It was found that the size of the reverse micelle structures affects the distribution of metal nano partices in polymer nano fibers. In order to distribute the metal nano particles homogeneously, the optimum size of reverse wormlike micelles was found to be between 420 and 450 nm.
3

Synthesis Of Silver Nanoparticles And Cable Like Structures Through Coaxial Electrospinning

Cinar, Simge 01 December 2009 (has links) (PDF)
The aim of this study is to demonstrate the possibility of production of nanocables as an alternative to the other one dimensional metal/polymer composite structures like nanowires and nanorods. There is no certain definition of nanocables / however they could be considered as assemblies of nanowires. Nanocable structure can be defined as a core-shell structure formed by a polymeric shell and a metal core that runs continuously within this shell. To produce nanocables, two main steps were carried out. Firstly, monodispersed silver metal nanoparticles to be aligned within the cable core were produced. Investigations on reduction reactions in the presence of strong and weak reducing agents and different capping agents revealed the importance of the kinetics of reduction in the production of monodispersed nanoparticles. Use of capping agents to give a positive reduction potential, resulted in the slow reduction rates that was critical for fine tuning of the final particle sizes between 1-10 nm. Hydrazine hydrate and oleylamine/ oleic acid systems were used as strong and weak reducing agents, respectively. By using weak reducing agent, monodisperse spherical silver nanoparticles with the diameter of 2.7 nm were produced. It was shown that particles with controlled diameter and size distribution can be obtained by tuning the system parameters. Secondly, particles produced as such were electrospun within the core of the polymer nanofibers and long continuous nanocables were produced. Polyvinyl pyrrolidone and polycaprolactone were used in shell part of nanocables. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), X-ray diffraction (XRD) and surface plasmon resonance spectroscopy (SPR) analyses were carried out in order to understand the mechanism by which the nanoparticles were reduced and for further characterization of the product.

Page generated in 0.0804 seconds