Lipid Tubule Research Leading to Electronic Composite Development

2/14/2003 - 16-03r
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Observations of small pieces of fat, such as one sees in a bowl of chicken soup, have led scientists at the Naval Research Laboratory (NRL) in Washington, D.C., to develop advanced composite materials for electronics applications. When these small globules of fat meet, they join spontaneously to form new shapes in a process called "self-assembly," which provides new building blocks for multifunctional materials applications. Bio-based molecular self-assembly is also leading to new applications in the areas of smart sensors, ultra-smart filters, long-term controlled release systems, and advanced displays.

Research and development programs at NRL, beginning in the 1980s, have progressed from initial observations of bio/molecular self-assembly in diacetylenic lipids, to the modification and subsequent observation of 500-nanometer (nm) hollow cylinders. Most recently these micro-sized cylinders have been used in electronic composites for cross-talk reduction in a Navy decoy called the NULKA. NULKA is an active, off-board, ship-launched decoy that counters radar-guided anti-ship cruise missiles.

Early work with diacetylenic lipids at NRL's Center for Bio/Molecular Science and Engineering led to the observation that these membrane-forming biomaterials have a low-temperature phase in which they form a hollow microcylinder with a high-aspect ratio. The length of these structures, called tubules, suggested that they might have use in electrical applications if they could be made electrically conducting. Substantial work was required before this was realized and involved coating the tubules with metal by an electro-less process. This electro-less coating applied about 200-300nm of copper, nickel or other highly conductive metals to the surface of the tubule, preserving its high-aspect ratio, but rendering it highly conductive.

Following successful application of the metal, an effort was begun to make dielectric composites of the metallic tubules in polymers and to explore the use of the resulting panels as an antenna isolation material. This work entailed the casting of hundreds of panels, with varying loading densities of tubules and other additives in several types of matrix polymer. To support this large fabrication effort, the synthesis of the lipid and its metallization technology were optimized to enable scale-up from the milligram to the hundreds-of-pounds level. All tests and evaluations were subject to the required costs, operational specifications and quality controls.

In the final stages of the program, designs were developed and panels were fabricated that met the needs of the NULKA decoy. The new composites contain advanced bio/nanoparticles with dielectric properties that give high isolation with a large bandwidth. In April 2002, a panel that met specifications was mounted on a test NULKA rocket for a captive-carry measurement off the coast of Florida. The test wassuccessful, meeting manufacturing and operational requirements, demonstrating that the performance of the tubule-based panel was equivalent electronically to that of the magnetic absorber it replaces, even though it weighs less than half of the weight.

The final product is a radar-absorbing panel for antenna isolation in the NULKA decoy that weighs less than half as much as the coating it replaces. The reduction in weight allows longer "dwell" time and improvements in performance for the decoy. The new material is a dielectric composite formed from ultra small, metal-coated biologically derived microtubes coated with copper and cast in polymer.

In ongoing work, preliminary evaluation of these bio-derived tubules for wearable antenna applications has been favorable.

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