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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

Spring 2014

First Advisor

Todd Emrick

Subject Categories

Polymer Chemistry

Abstract

Encapsulation of materials can be performed through the stabilization of fluid-fluid interfaces and the formation of emulsion droplets, which is commonly achieved with surfactants, including small molecules and polymers, as well as particles that are, typically, micron-scale in diameter. The worked contained in this dissertation centered on droplets that are stabilized by nanoparticles, including metallic nanoparticles and semiconductor quantum dots, which bring the conductive and fluorescent properties inherent to such nanoparticles into the droplet construction.

Double emulsion droplets, both oil-in-water-in-oil (o/w/o) and water-in-oil-in-water (w/o/w) were formed using nanoparticles as the only surfactant in solution. Different types of nanoparticles were found to have unique surfactant properties - hydrophobic CdSe quantum dots stabilized the water-in-oil interface, while tetra(ethylene glycol)-functionalized gold nanoparticles localized at the oil-in-water interface. Such double emulsion droplets were formed with a broad polydispersity of size by hand mixing, while well-defined (more near monodispersed) droplets were obtained by a microcapillary flow focusing technique.

Triggered mechanisms were designed and implemented with functional nanoparticle ligands possessing a photosensitive linker. Such a ligand design allowed for emulsion inversion to occur upon irradiation of stabilized emulsions. For instance, an initially hydrophobic ligand was cleaved by irradiation with 365 nm UV-light to generate carboxylic acid functionality at the periphery of the nanoparticles. This change in wetting properties provided a facile route to emulsion inversion. Starting from a water-in-oil emulsion stabilized with functionalized CdSe nanoparticles, an oil-in-water emulsion was obtained after irradiation with 365 nm UV-light. These types of responsive droplets are novel, interesting systems that proved successful for triggered/controlled release.

Robust capsules were formed using the self-polymerization properties of dopamine. The formation of these robust capsules was achieved in the absence of any ligand exchange chemistry and confirmed by fluorescence confocal microscopy. The permeability of these capsules was studied by release of water-soluble polymer-based dyes. Small molecules, such as calcein, passed through the polydopamine membrane, while high molecular weight molecules did not permeate.

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