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Speakers and Abstracts
All presenters are seniors in Chemical Engineering at the University of Washington, and the presentations are on their current independent research projects.
Joseph Crowell - Adhesion in Fiber-Reinforced Composites
A polymeric composite is a combination of two discrete substances, one of which is a polymer, and is generally engineered to be both strong and light weight. Fiber-reinforced composite materials contain fibers (usually glass or carbon) embedded inside the structural matrix, where the matrix transmits most of the load to the fibers. Unfortunately, polymeric composites often exhibit poor adhesion between the matrix and the fibers, leading to poor stress transfer. One feasible way to increase adhesion is to add an interphase structure to induce mechanical interlocking. For this research, silica particles are attached to the fibers by electrostatic adhesion. The particles are functionalized using either tri-aminosilane or polyethyleneimine, and the fibers (E-glass) are functionalized using 3- glycidoxypropyltrimethoxysilane (GPS). By keeping the pH above the point of zero charge (PZC) of the E-glass, but below the PZC of the coated silica nano-particles, the fibers and particles will electrostatically adhere to one anther. A fiber fragmentation test can be performed to determine the level of IFSS (interfacial shear strength) achieved. The IFSS provides a measurement of the fiber–matrix adhesion. Not only should nano-particles help increase adhesion, they also should help reduce fiber-fiber contact, which has been shown to lower the IFSS significantly. The present study concerns E-glass fibers embedded in an epoxy matrix. Once the appropriate conditions have been met for E-glass fibers, the theory and results can then be extended to carbon fiber - epoxy systems.
Emily Hollenbeck - Synthesis and Characterization of New N-type Organic Semiconductors for Photovoltaic Applications
Organic photovoltaics (OPVs) are a promising low-cost option in developing renewable energies. OPVs are solar cells made from organic semiconductors instead of the more traditionally used inorganic semiconductors such as silicon. OPVs have several advantages including: low cost, ease of processing, physical flexibility, and highly tunable properties. Therefore, if the efficiency of OPVs can be increased, they could become a major, inexpensive renewable energy source. Electron-accepting materials used in OPVs have traditionally been fullerene-based due to their high electron mobility. However, fullerenes contribute little to light harvesting in an OPV as they have negligible absorption in the solar spectrum. Thus, our goal was to develop new electron-accepting materials for OPVs that absorb significantly in the solar spectrum as a means to increase light harvesting and therefore OPV efficiency. A series of novel oligomers with an oligothiophene-naphthalene diimide (NDI) structure was synthesized. All oligomers exhibited absorption in the visible region with band gaps ranging from 1.39 eV to 2.06 eV, and could therefore contribute to light harvesting in an OPV. Solution-processed solar cells using the new oligomers as the electron-acceptors showed power conversion efficiencies up to 1.5%. Overall, these new materials exhibited that non-fullerenes can function as the electron-accepting material in OPVs while contributing to light harvesting. This approach therefore shows promise for increasing OPV efficiency to make OPVs a viable, cost-effective renewable energy source.
David Bergsman - The Effect of Silane Treatments on the Surface Properties of Silica
A growing number of applications seek to use electrostatic effects in non-polar media. However, the science behind particle charging in such systems is not fully understood. Previous work has suggested that the presence of surface hydroxyl groups, when combined with certain surfactants, can induce charging of the particles. These surfactants also serve to prevent particle aggregation through steric stabilization. However, dispersing these particles typically requires extended sonication or some other dispersive technique. One possible solution for promoting dispersion is to first hydrophobically surface-treat the particles. Unfortunately, this process has the potential to remove the hydroxyl groups necessary for particle charging. Therefore, we are investigating the effects of surface modification on particle hydrophobicity and chargeability. Silica particles on the micron and submicron scale were surface treated with tri-methoxy(octyl) silane and methoxy(dimethyl)octylsilane in order to create hydrophobic silica particles with varying amounts of hydroxide groups on their surfaces. The resulting surface energy and acid/base characteristics of these particles were then tested using Inverse Gas Chromatography (IGC), with the intent of comparing these properties to the particles' chargeability. This was assessed by measuring their electrophoretic mobilities using a Zeta Potential Analyzer. Our results indicated that particles could be made both hydrophobic and chargeable after surface treatment. However, further investigation is required in order to better understand the mechanism behind this charging. If the surface modification can preserve particle chargeability while adding a steric barrier, this process could be used to reduce dispersion time for charged particles in non-polar media.
John Geil - Titania-Stabilized Pickering Emulsions for Skin Care Products
Pickering Emulsions may be formed by adsorbing particles to the interface of the liquid droplet. These particles increase stability of the emulsion by holding droplets further apart than the critical film thickness, at which the droplets coalesce. A study of the use of silane-treated, hydrophobic, titanium dioxide particles to stabilize an isododecane in water emulsion, for the purpose of pigment (titanium dioxide) deposition on skin, was conducted. Results are shown for the formation of these isododecane in water Pickering Emulsion systems, using shear stress mixing. Mixing methods results were optimized to form emulsions without entraining air. Also results for the silane treatment of bare titanium dioxides particles, to increase hydrophobicity, are presented. As a function of reaction time, the hydrophobicity of titanium dioxide particles can be tuned to force the particles to the interface of the isododecane droplets. Furthermore included is an overview of stability for the Pickering Emulsions. By comparing the coalescence of the particle-stabilized isododecane droplets to naked isododecane droplets, it was observed the particle stabilized emulsion was stable towards coalescence, while the naked isododecane droplets coalesced rapidly. Using optical microscopy, these titanium dioxide stabilized emulsions are shown to form and enhance stability of the emulsion.