Type of Document Dissertation Author Ridley, Jason Ian URN etd-02192010-144842 Title Improvement of the Optical and Mechanical Properties of Silica Nanoparticle Ionic Self-Assembled Multilayer Anti-Reflection Coatings on Glass and Polycarbonate Substrates Degree PhD Department Physics Advisory Committee
Advisor Name Title Heflin, James R. Committee Chair Ritter, Alfred L. Committee Co-Chair Khodaparast, Giti A. Committee Member Soghomonian, Victoria Committee Member Keywords
- UV Irradiation
- Glass Fibers
- Diazo- Resin (DAR)
- Silica Nanoparticles
- Ionic Self-Assembled Multilayers (ISAM)
Date of Defense 2010-02-05 Availability unrestricted AbstractA fundamental requirement in agricultural trade is that imported products are safe, and do not pose a risk to human, animal and plant health. To address this issue, all countries maintain measures to ensure that imported food is safe for consumers, and to prevent the spread of disease among animals and plants. These measures, by their nature, can affect competitiveness by increasing the costs of imports or prohibiting them altogether. To ensure that these measures are used for their intended purpose and not as protectionist measures, WTO member countries signed the Agreement on the Application of Sanitary and Phytosanitary measures.This thesis presents the characterization of the optical and mechanical properties of silica nanoparticle films fabricated by ionic self-assembly, also known as layer-by-layer (LbL) deposition. Utilizing electrostatic attraction of oppositely-charged materials permits uniform and rapid growth of the constituents onto planar and curved surfaces. In this work, silica nanoparticles are adsorbed onto glass and polycarbonate substrates, as well as micron-scale glass fibers, with the purpose of improving the optical quality of the respective media.
Several methods are presented to improve the adhesion and cohesion of silica nanoparticle films on glass substrates. In the first method, the substrate and nanoparticle surfaces are coated with materials containing sulfonate end groups. Next, a photo-reactive polycation known as diazo-resin (DAR) is used in ISAM deposition with the modified silica nanoparticles. Subsequent exposure to UV converts the ionic bonds between the DAR and sulfonate groups into covalent ones. The second method to improve the mechanical strength is to heat the ISAM silica nanoparticle film at a high enough temperature (500 °C) to remove the polymer and partially fuse the nanoparticles. This technique is known as calcination and is shown to significantly improve the mechanical robustness of the film without compromising the optical properties. The final method involves the deposition of precursor and capping polymer layers around bulk silica nanoparticle films with both bilayer and quadlayer designs. The addition of these polymer layers improves the surface contact between adjacent nanoparticles but reduces the film porosity and consequently the optical transparency. Currently the calcination technique is the only one that significantly improves the film adhesion and cohesion, but suggestions are offered to potentially improve the performance of films made by the other two methods.
An alternative way to functionalize polycarbonate substrates for silica nanoparticle ISAM deposition is also presented. The molecular structure of polycarbonate at the surface can be modified by exposing it to deep UV (lambda = 185, 254 nm). By doing so, the surface becomes populated with carboxylate species, and thus permits ISAM deposition of poly(allylamine hydrochloride) (PAH) and silica nanoparticles. A variety of spectroscopic methods show that the molecular structure is changed by this procedure, and SEM shows that UV treatment improves the uniformity of ISAM films on polycarbonate.
Finally, PAH/silica nanoparticle ISAM films are deposited onto glass fibers. The fibers are used for mechanical reinforcement of polymer composite optical media. The role of the nanoparticle film on the fibers is to reduce light scattering at the interfaces of materials with different thermo-optic coefficients, in other words, transmittance losses associated with changes in temperature. Fiber bundles coated with silica nanoparticles suffer from unacceptable levels of aggregation, and hence do not currently improve the transmittance over the temperature spectrum. Some evidence is presented, however, to suggest that the transparency can be improved if fiber aggregation during ISAM deposition can be avoided.
A growing number of studies attempt to quantify the effects of SPS regulations on international trade flows. However, precious little research is dedicated to determining the effects of specific phytosanitary regulations on trade flows and, more importantly, questions regarding SPS regulations and their impact as “trade barriers” or “trade catalysts” remain to be settled.
This thesis contributes to existing literature in two ways. First, a comprehensive and user friendly database on specific phytosanitary regulations faced by U.S. exports of onions, peas, walnuts, apples, cherries, grapes, peaches/nectarines, oranges and strawberries to 176 countries is developed for the period 1999-2009. Second, this database is used for an empirical investigation to determine how existing SPS regulations affect U.S. fruit and vegetable exports.
The results indicate that initially, phytosanitary treatments act as “barriers” to trade. However, as exporters’ experience grows, the negative impact of treatments is reduced and eventually eliminated.
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