Doctor of Philosophy (PhD)
Self-assembly is scientifically interesting, technologically important, and sometimes life-threatening. A striking example: Alzheimer’s disease is caused by the self-assembly of the â-amyloid fragment of amyloid precursor protein. Such natural amphiphiles normally are very expensive and complicated to isolate. Synthetic mimics that are much cheaper and easier to prepare can facilitate the development of efficient characterization methods, even as they suggest new materials science applications. Two-directional arborols are synthetic bolaform amphiphilic dendrimers. They dissolve in hot water and form reversible gels at room temperature. Bundles of fibrils, which are made by self-assembly of arborols, are found in the gels. The properties of the fibrils are characterized with scattering and microscopy from one hundred micron meters scale to molecular level at nano meter size. The porous nature inside the gels is investigated by comparing the diffusion of fluorescently labeled dextrans in arborol gels with that in water. The time dependence of the self-assembly of two-directional arborols from short fibrils to long ones is tracked by microscopy and light scattering. Addition of a one-directional inhibitor slows the self-assembly. To understand the mechanism, the properties of the one-directional arborols at the air-water interface are addressed. The self-associated arborol fibrils can be disassembled by growing gold nanoparticles in the arborol gels or solutions. In a basic arborol solution or gel, gold nanoparticles with an average diameter below 50 nm are formed after adding a diluted gold ion solution. The arborols act as both reducing agents and stabilizers in the formation of gold nanoparticles. Additionally, the long and thin fibrils in the arborol gel/solution are dismantled. As applications, an attempt to build nano-tunnels in the cross-linked poly(N-isopropyl acrylamide), a temperature sensitive hydrogel, PNIPAM gel, by replacing the preloaded arborol fibrils with water is discussed. Finally, encapsulation of the self-assembly fibrils in giant unilamellar vesicles (GUVs) is tried. As supplemental information, the size variance of liposomes at different lipids/arborols ratios is studied by fluorescence photobleaching recovery (FPR) and light scattering.
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Sun, Jirun, "Self-Assembly and Its Inhibition in Bolaform Amphiphilic Dendrimers" (2006). LSU Doctoral Dissertations. 2989.