Smaller Means Better

The composition of seashells, bones, and teeth serves as evidence that nature already has the upper hand in creating a host of materials from individual atoms and molecules. While humankind has not yet achieved true “molecular manufacturing”—manipulating and assembling individual atoms on a large scale—scientists are closing in on this goal around the world and here in Troy.

An expert in nanotechnology for more than 15 years, Richard W. Siegel works with materials made up of common atoms arranged in grains of less than 100 nanometers in diameter that are 10,000 times smaller than grains in conventional materials.

“Lots of people can now make nanoscale building blocks to create nanostructures,” Siegel says. “The question is how do you assemble them to create new materials and novel devices. That’s exactly what our researchers will do.”

Siegel began researching nanoparticles in the mid-1980s at Argonne National Laboratory, southwest of Chicago, where he pioneered the development of nanoceramics more than a decade ago. In 1989, he co-founded Nanophase Technologies Corp., one of the first nanotechnology-based businesses.

As head of the Rensselaer Nanotechnology Center, Siegel will oversee more than 30 researchers whose work spans nearly every discipline on campus from materials science, physics, chemistry, and biology to biomedical, chemical, and electrical engineering, and computer science.

In biotechnology research, for example, Rena Bizios, professor of biomedical engineering, and Siegel are investigating the potential of nanoceramics and nanoceramic/polymer composites as bone implants.

“Nanophase materials have great potential which, to date, remains unexplored for many biomedical and tissue engineering applications,” Bizios says. “The Rensselaer Nanotechnology Center is providing the resources for pioneering research in the emerging field of nanophase biomaterials.”

In this project, Bizios and Siegel have used nanoceramics of alumina and titania alone or in nanocomposites with such polymers as polyactic acid or polymethylmethacrylate. The goal is to formulate novel biomaterials with enhanced mechanical properties that are compatible with cells.

One finding their research has produced so far is that the nanoceramics and nanocomposites promote selectively enhanced functions of osteoblasts (bone-forming cells). This includes cell adhesion, proliferation, and deposition of calcium-containing minerals, an indication of new bone formation in the laboratory setting.

“These are models for creating novel implant materials. We’re not only looking at mechanical behavior, but how living cells interact with materials,” Siegel says. “Cells interact very differently with nanoscale materials. They react selectively and in the right way.”

Smaller Is Better

An important component of the NSF Center will be an effort to excite and educate a diverse cadre of young people in grades K-12 and beyond. Linda Schadler, associate professor of materials science and engineering at Rensselaer, will lead the outreach activities. Photo: Gary Gold

Rensselaer researchers, such as Linda Schadler and Siegel, also are working toward engineering new nanocomposite materials that resist scratching, stand up to twisting and stretching, survive high temperatures, are stronger and more durable, and insulate electrical current far better than those materials in general use today.

The chemical composition of nanophase materials is the same as their conventional counterparts, but the particles or crystals that serve as basic building blocks of the material are much smaller. The smaller-size building blocks alter a material’s mechanical, optical, electrical, and magnetic properties, and create, for example, copper five times harder than its conventional form and ceramics that bend instead of breaking.

Much of Schadler’s research revolves around the custom design of polymer composites. Her work includes embedding nanomaterials into polymer and ceramic matrices.

“Several features of nanoparticles can be exploited to control properties,” Schadler explains. “First, nanoparticles have a significantly larger surface area than microscale particles. Therefore, the volume of polymer affected by the nanoparticles is much larger than for micron-scale fillers. In addition, nanoparticles can be small enough that they don’t scatter light. This creates an opportunity for improving the properties of transparent polymers without significantly decreasing their transparency.”

Such research could result in better plastic windshields for military aircraft. In one project, Schadler is adding alumina nanoparticles to polymethylmethacrylate (PMMA), a polymer that is sometimes marketed as Plexiglas. “We have been able to increase the ductility of PMMA by an order of magnitude,” she says. In other composite systems, Schadler and her colleagues have increased the scratch resistance while maintaining optical clarity.

Carbon Nanotubes: Wire of the Future

One nanoparticle that has been the focus of much attention is the carbon nanotube. Pulickel Ajayan, associate professor of materials science and engineering, is at the forefront of research surrounding these quirky “nanoscopic” cylinders.

Carbon nanotubes—long, thin cylinders of carbon, each a mere 1 to 25 nanometers in diameter—were discovered in 1991 by Sumio Iijima while he was conducting work as a senior research fellow at NEC Corp. in Japan. By discovering a technique to insert metal into the hollow of carbon nanotubes, Iijima created what could be the tiniest wire ever made.

A year later, Ajayan and a colleague, Thomas Ebbesen, both working in Iijima’s lab, showed how nanotubes could be produced in bulk by controlling the heating conditions by which they are made. This paved the way to an explosion of research into the physical and chemical properties of carbon nanotubes in laboratories all over the world.

Carbon nanotubes are macromolecules, unique for their size, shape, and remarkable physical properties. Their structure comprises a sheet of carbon atoms in a honeycomb arrangement, which is the basic structure of graphite. Graphite is a soft, black lustrous form of carbon that conducts electricity and is used in making lead pencils, as a lubricant, and as a moderator in nuclear reactors.

“The carbon nanotube is considered as the most perfect, strongest fiber ever made,” says Ajayan. “The combination of structure, topology, and dimension creates a host of physical properties in nanotubes that are paralleled by few known materials and make them a unique material with a whole range of promising applications.”

Unlike conventional graphite, the carbon nanotube is expected to be semiconductive or metallic, depending on its specific structure. With these characteristics and molecular size, the carbon nanotube may revolutionize microelectronic devices.

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