GAS FLOW CHARACTERISTICS OF VARIOUS DISCRETE JET, CLOSE-COUPLED GAS ATOMIZATION NOZZLE DESIGNS. JAMES CRONIN (Clemson University Clemson, SC 29632) IVER E. ANDERSON (Ames Laboratory, Ames, IA, 50011)

To gain a further understanding behind the gas flow characteristics in discrete jet, close-coupled gas atomization, high speed photography, aspiration testing, and velocity probe testing have been conducted on gas-only flows from various nozzle geometries currently used for experimental atomization processes. Experiments indicate that a certain degree of control over the atomization process can be obtained by utilizing the gas-only flow trends that arise from the design variables of these nozzles. The variables considered were: atomizing gas composition, nozzle jet configuration (angle, number, and size), and melt tube insert parameters (length and chamfer angle). These were arranged into a test matrix to isolate gas flow and pressure trends associated with each of the individual variables. Initial results from a combination of Schlieren images and aspiration pressure data were obtained for the formation of the Mach disk in relation to operating pressure and nozzle geometry. The findings show that a shorter insert tube length (2.286 mm) is a major factor for forming a Mach disk at a lower pressure with a minor factor being a wide jet apex angle (45 ). These and other resulting fluid flow trends can now be used in conjunction with future research to enable gas atomization process designs that minimize mean size of the powders produced, reduce the standard deviation of the powder batch, and improve the overall efficiency.

Initialization, Optimization and Integration of Ultra-High Speed Photography for Rapid Solidification Processes. DAVID SAUER (University of Missouri-Rolla Rolla, MO 65401) R. WILLIAM MCCALLUM (Ames Laboratory, Ames, IA, 50011)

An Ultra-High Speed camera has been acquired by the Materials and Engineering Physics Program at Ames Laboratory to study rapid solidification processes. The camera, a Phantom v7.1 manufactured by Vision Research Inc., is state of the art in digital rapid photography. The camera is capable of 160,000 digital images per second at a resolution of 32 x 32 pixels. Using melt spinning as the model process, the image acquisition system has been optimized for optics, image size and rate (320 x 320 pixels at 8,000 images per second), and attached data collection. A matrix of rapid solidification runs were performed and analyzed for characteristic flow parameters as derived from acquired images. Representative images from the experimental matrix of solidification runs, spanning multiple parameters, were analyzed for dynamic fluid flow dimensions. Two main variables were verified as influences on the melt pool characteristics, wheel speed and ejection pressure. When wheel speed increased, the melt pool length showed a hyperbolic slope with the melt pool length approaching a minimum value of 2 mm. When ejection pressure was changed, the melt pool height changed in a characteristic inverse linear fashion. With these results, the rapid solidification process will be better understood and the characteristics of the product will be more easily identifiable with the parameters applied during the melt-spin process.

Photonic Bandgap Material Fabrication via Two-Polymer Micro-Transfer Molding. XUEYING QIN (Carleton College Northfield, MN 55057) KRISTEN CONSTANT (Ames Laboratory, Ames, IA, 50011)

Photonic bandgap materials, also known as photonic crystals, are materials that exhibit a photonic bandgap, which is a phenomenon that prevents a specific set of wavelengths of electromagnetic radiation from propagating through the crystal. Two-polymer micro-transfer molding is a novel technique for the fabrication of these crystals, and can be performed much more cost-effectively with a minimal loss in efficiency than traditional photonic crystal fabrication techniques. By using pre-made silicon wafer molds, a mixture of polydimethylsiloxane (PDMS) is poured onto the pattern and the pattern is then cured in an oven for several hours, allowing the PDMS to solidify. When removed, the PDMS mold now has the pattern imprinted in it, in the form of many small channels in its surface, whose size and spacing depend on the desired wavelength bandgap. These channels are then filled with polyurethane (PU) and are then cured under ultraviolet light to allow the PU to solidify. The sample area is now coated with optical cement (PA), a glass cover slip is attached, and then the sample is once again cured in a UV oven. Afterwards, the PDMS is peeled off and the remaining PU structure is transferred onto the glass slide. The work done by this group aims to improve the PU-stage of sample fabrication. This method is desirable in that it does not need to be performed in clean-room facilities, and therefore is far more cost-effective than traditional methods. The single-layer samples can then be used in 3-dimensional crystals via a method of stacking also being developed by this research group. This is all a part of a larger effort to develop cost-effective, efficient techniques for the fabrication of 3D photonic bandgap materials.

Synthesis and Characterization of Glucose-Sensitive Diblock Copolymers. CHRISTOPHER WONG (Northwestern University Evanston, IL 60201) SURYA MALLAPRAGADA (Ames Laboratory, Ames, IA, 50011)

A diblock copolymer consisting of poly(ethylene glycol) (PEG) and 4-(1,6 dioxo-2,5-daza-7-oxamyl)phenylboronic acid (DDOPBA), has been synthesized via reversible addition fragmentation transfer (RAFT) polymerization. The DDOPBA polymer is an anionic polyelectrolyte with a pKa ~ 7.8. In aqueous solutions, glucose forms a charged complex with the phenylboronic acid moiety of the DDOPBA resulting in a dual hydrophilic-hydrophilic block copolymer. In the absence of the glucose the DDOPBA block is uncharged and becomes insoluble, resulting in the formation of micelles with DDOPBA cores and PEG corona structure. The molecular characteristics of this novel block copolymer were characterized with 1H NMR and size exclusion chromatography. Reversible, glucose dependent micellization in aqueous solution, around physiological pH, was shown with multi-angle laser light scattering (MALLS) and quasi-elastic light scattering (QELS). This material has potential applications in food processing and sensing technologies.