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Supramolecule-Directed Self-Assembly of Nanorods

  • Author(s): Thorkelsson, Kari
  • Advisor(s): Xu, Ting
  • et al.
Abstract

In this dissertation, a procedure for ordering nanorods both spatially and orientationally using a diblock copolymer-based supramolecule is developed and examined in bulk and thin film. Anisotropic nanomaterials display a number of properties that could prove useful in various applications including photovoltaics, magnetic storage, and sensors. However, effective use of these properties often require control over the spatial organization of the particles: some applications, e.g. for use in magnetic storage, require well-defined arrays of particles, while others, e.g. as a method of mechanical strengthening, require interconnected networks. Furthermore, the anisotropy in the properties that arises from the anisotropic structure of the nanomaterials only manifests on the macroscale if the particles are oriented on a macroscopic scale. Thus, to be able to fully employ the properties of these nanomaterials, it is necessary to control both spatial arrangement and orientation over large areas.

This method, employing a diblock copolymer-based supramolecule to control and direct nanoparticle assembly, was first applied to assemble isotropic nanoparticles. It was used to confine nanoparticles to a sheet with a thickness approaching that of a single nanoparticle, as well as in hexagonal arrays. A variety of small molecules, nanoparticles, and thermal treatments were tested, demonstrating the robustness and versatility of the system.

Using the knowledge acquired from coassembly with isotropic nanoparticles, the system was applied toward assembling anisotropic nanorods. First, nanorods approximately thirty nanometers in length and four in diameter were arranged into arrays, sheets, and interconnected networks by varying the relative volume fractions of the supramolecular blocks. Then, this process was extended to nanorods of different lengths and at various concentrations and thermal treatment conditions, exposing how the kinetics of assembly affect the process.

Finally, after examination of nanorod assembly in bulk composites, the system was used to form thin film assemblies of nanorod-supramolecule composite. The geometric constraints inherent in the thin film morphology introduce new energetic factors that must be accounted for during assembly. By adjusting nanorod length and concentration, end-to-end assemblies of nanorods over large areas was accomplished.

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