Manufacturing & Prototyping

Fabricating PFPE Membranes for Capillary Electrophoresis

Precisely sized and positioned holes are defined by photomasks. A process has been developed for fabricating perfluoropolyether (PFPE) membranes that contain microscopic holes of precise sizes at precise locations. The membranes are to be incorporated into “laboratory-on-a-chip” microfluidic devices to be used in performing capillary electrophoresis.

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Fabricating PFPE Membranes for Microfluidic Valves and Pumps

This process contributes to development of “laboratory-on-a-chip” devices. A process has been developed for fabricating membranes of a perfluoropolyether (PFPE) and integrating them into valves and pumps in “laboratory-on-a-chip” microfluidic devices. Membranes of poly(tetrafluoroethylene) [PTFE] and poly(dimethylsilane) [PDMS] have been considered for this purpose and found wanting. By making it possible to use PFPE instead of PTFE or PDMS, the present process expands the array of options for further development of microfluidic devices for diverse applications that could include detection of biochemicals of interest, detection of toxins and biowarfare agents, synthesis and analysis of proteins, medical diagnosis, and synthesis of fuels.

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Structural/Radiation-Shielding Epoxies

Pendant aliphatic groups are incorporated as integral parts of molecular structures. A development effort was directed toward formulating epoxy resins that are useful both as structural materials and as shielding against heavy-ion radiation. Hydrogen is recognized as the best element for absorbing heavy-ion radiation, and high- hydrogen-content polymers are now in use as shielding materials. However, high- hydrogen-content polymers (e.g. polyethylene) are typically not good structural materials. In contrast, aromatic polymers, which contain smaller amounts of hydrogen, often have the strength necessary for structural materials. Accordingly, the present development effort is based on the concept that an ideal structural/heavy-ion-radiation-shielding material would be a polymer that contains sufficient hydrogen (e.g., in the form of aliphatic molecular groups) for radiation shielding and has sufficient aromatic content for structural integrity.

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Modal Vibration Analysis of Large Castings

Massive objects can be tested in situ, without precisely controlling boundary conditions. The art of experimental modal vibration analysis (MVA) has been extended to apply to large castings. This extension was made to enable the use of experimental MVA as a relatively inexpensive, simple means of assessing the internal structural integrity of tread shoes of crawler transporters used to move spacecraft to the launch pad at Kennedy Space Center. Each tread shoe is made from cast iron and weighs about a ton (has a mass ≈907 kg). The present extended version of experimental MVA could also be applied to other large castings. It could be especially useful to manufacturers as a means of rapidly discriminating against large castings that contain unacceptably large concentrations of internal defects.

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Laser Ablation Increases PEM/Catalyst Interfacial Area

Increased interfacial area is expected to result in improved fuel-cell performance. An investigational method of improving the performance of a fuel cell that contains a polymer-electrolyte membrane (PEM) is based on the concept of roughening the surface of the PEM, prior to deposition of a thin layer of catalyst, in order to increase the PEM/catalyst interfacial area and thereby increase the degree of utilization of the catalyst. The roughening is done by means of laser ablation under carefully controlled conditions. Next, the roughened membrane surface is coated with the thin layer of catalyst (which is typically platinum), then sandwiched between two electrode/catalyst structures to form a membrane/electrode assembly.

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Diamond Machining of an Off-Axis Biconic Aspherical Mirror

Complex shapes can be produced at relatively low costs. Two diamond-machining methods have been developed as part of an effort to design and fabricate an off-axis, biconic ellipsoidal, concave aluminum mirror for an infrared spectrometer at the Kitt Peak National Observatory. Beyond this initial application, the methods can be expected to enable satisfaction of requirements for future instrument mirrors having increasingly complex (including asymmetrical), precise shapes that, heretofore, could not readily be fabricated by diamond machining or, in some cases, could not be fabricated at all.

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Alternative Packaging for Back-Illuminated Imagers

Electrical contacts are made accessible from the back side. An alternative scheme has been conceived for packaging of silicon- based back-illuminated, back- side-thinned complementary metal oxide/semiconductor (CMOS) and charge-coupled-device image-detector integrated circuits, including an associated fabrication process. This scheme and process are complementary to those described in “Making a Back- Illuminated Imager With Back-Side Connections” (NPO-42839), NASA Tech Briefs, Vol. 32, No. 7 (July 2008), page 38.

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