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News & Analysis Pulickel Ajayan Pioneers Nanotech At Rennselaer   
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“Somewhere along the way, science became a very logical, romantic, and mature thing to do. … I can be imaginative, flexible with my time, and influence young people in a positive way… I can be working and dreaming at the same time.” Pulickel Ajayan.

29 November 2005 -- If he had not become a scientist, Pulickel M. Ajayan, the Henry Burlage Professor of Materials Science and Engineering at Rensselaer Polytechnic Institute, and a native of the ancient historic town of Kodungallur in Kerala, would perhaps have become a poet or a film director. That’s because, as he once acknowledged, “I am always looking for simple and beautiful things in science, be it a process, a structure, or a model.”

So, twenty years after obtaining his B.Tech from Banaras Hindu University, and 15 Years after his Ph.D from Northwestern University, Ajayan has evolved into a pioneer in the field of carbon nanotubes or, more specifically, ‘Fabrication of Organized Carbon Nanotube Architectures.’

Over the years, Ajayan has been involved in several of the initial works on nanotubes, in particular the large-scale synthesis of nanotubes and opening and filling of nanotubes. Ajayan’s research is focused on building functional architectures with carbon nanotubes, creating multi-functional nanocomposite materials and hybrid nanoscale biomaterial systems.

And while looking for the simple and the beautiful in science he’d rather not spend large chunks of time “writing research proposals to raise money, too much travel, and many unproductive meetings” that are part of the scientist’s role. “In the long run, I would like to create materials that are smart and responsive, more like biological systems; where structure and function have a symbiotic relationship. In the short term, I would like to build architectures with carbon nanotubes.” In fact, Ajayan, who is a professor of materials engineering at Rennsselaer Polytechnic Institute can boast a long catalog of nanotube-based materials with tantalizing properties, all of which are the outcome of collaborations with other institutions worldwide.

"If there was one material that I would hold up and say 'This is it' as far as nanotechnology is concerned, that is carbon nanotubes," says Ajayan who has been on the faculty at Rennselaer since 1997.

Discovered in 1991, these tiny structures are light and flexible, yet one hundred times stronger than steel. But they're very hard to control. "We know the structure of nanotubes," says Ajayan, "but the question is, can we really put them together in the way we want?"

Professor Ajayan's research interests are mainly focused on the synthesis of nanostructures, the study of their structure and properties in relation to size and confinement. He has demonstrated several possibilities for using these quasi one dimensional structures as templates and molds for fabricating nanowires, composites, and novel ceramic fibers. Major goals of his research include producing macro assemblies made of nanostructures for applications, understanding growth mechanisms of nanostructures and designing new structures and multifunctional nanocomposites.

It's interesting too that he is mentoring a number of postgraduate and post doctoral students of Indian origin such as Balvinder Gogia, Saikat Talapatra, Kaushal Rege, Guna Vishwanathan, Aravind Vijayaraghavan, Nachiket Raravikar, and Nirupama Chakrapani in his intensely productive lab.

LATEST FINDING

The latest finding from the Ajayan lab is that films of aligned carbon nanotubes can act like a layer of mattress springs, flexing and rebounding in response to a force. But unlike a mattress, which can sag and lose its springiness, these nanotube foams maintain their resilience even after thousands of compression cycles.

Carbon nanotubes are made from graphite-like carbon, where the atoms are arranged like a rolled-up tube of chicken wire. Ajayan and a team of researchers at the University of Hawaii at Manoa and the University of Florida subjected films of vertically aligned nanotubes to a battery of tests, demonstrating their impressive strength and resilience.

"These nanotubes can be squeezed to less than 15 percent of their normal lengths by buckling and folding themselves like springs," says lead author Anyuan Cao, who did much of the work as a postdoctoral researcher in Ajayan’s lab and is now assistant professor of mechanical engineering at the University of Hawaii at Manoa. After every cycle of compression, the nanotubes unfold and recover, producing a strong cushioning effect.

The thickness of the nanotube foams decreased slightly after several hundred cycles, but then quickly stabilized and remained constant, even up to 10,000 cycles. When compared with conventional foams designed to sustain large strains, nanotube foams recovered very quickly and exhibited higher compressive strength, according to the researchers. Throughout the entire experiments, the foams did not fracture, tear, or collapse.

And their intriguing properties do not end there. Nanotubes also are stable in the face of extreme chemical environments, high temperatures, and humidity all of which adds up to a number of possible applications, from flexible electromechanical systems to coatings for absorbing energy.

Carbon nanotubes have enticed researchers since their discovery in 1991, offering an impressive combination of high strength and low weight. Now Ajayan’s study suggests that they also act like “super-compressible” springs, opening the door to foam-like materials for just about any application where strength and flexibility are needed, from disposable coffee cups to the exterior of the space shuttle.

“Carbon nanotubes display an exceptional combination of strength, flexibility, and low density, making them attractive and interesting materials for producing strong, ultra-light foam-like structures,” says Ajayan.

Carbon nanotubes are made from graphite-like carbon, where the atoms are arranged like a rolled-up tube of chicken wire. Ajayan at Rensselaer and a team of researchers at the University of Hawaii at Manoa and the University of Florida subjected films of vertically aligned nanotubes to a battery of tests, demonstrating their impressive strength and resilience.

The thickness of the nanotube foams decreased slightly after several hundred cycles, but then quickly stabilized and remained constant, even up to 10,000 cycles. When compared with conventional foams designed to sustain large strains, nanotube foams recovered very quickly and exhibited higher compressive strength, according to the researchers. Throughout the entire experiments, the foams did not fracture, tear, or collapse.

Ajayan and researchers from the University of Hawaii at Manoa previously developed tiny brushes with bristles made from carbon nanotubes, which could be used for tasks that range from cleaning microscopic surfaces to serving as electrical contacts. And in collaboration with scientists from the University of Akron, Ajayan and his team created artificial gecko feet with 200 times the sticking power of the real thing.

In collaboration with Ganapathiraman Ramanath, Ajayan was the first to achieve the unprecedented, specific, and controlled nanotube growth.

Next-generation computer chips, integrated circuits, and the microelectro-mechanical (MEMS) devices that power them depend upon carbon nanotubes that can be grown up, down, sideways, and in all three dimensions. Their research, reported in the journal Nature, paves the way for Lilliputian devices that depend on tiny networks and architectures.

The method is based on a selective growth process that allows the nanotubes to grow perpendicular to the silica-coated substrate. By chiseling the silica into predetermined shapes, the researchers are able to precisely control and direct the nanotube growth. Their use of gas phase delivery of a metal catalyst, essential for nanotube growth, makes their growth process more flexible and more easily scalable than conventional methods. "It's a simple and elegant process that provides unprecedented control over nanotube growth," Ajayan says.

Ajayan and G. Ramanath were the first to combine formerly disparate areas of research to grow and direct the assembly of nanotubes.

Ajayan says that while he is pleased with the interdisciplinary nature of research in areas like nanotechnology, he is also concerned about the “growth of forces that dictate the direction of research and scientific discovery.” He notes that “the power of funding agencies and big journals, and the perception that big programs mean better research has escalated in recent years.”

Meanwhile, Saurabh Agrawal, a graduate student of G. Ramanath, this week presented a paper on Carbon nanotubes for water treatment. They report that while activated carbon has long been the standard for removing organic contaminants from drinking water, carbon nanotubes have significant potential as better materials for water purification. The study is in collaboration with Banaras Hindu University.

francisassisi@hotmail.com


Francis C. Assisi will be on vacation during December.


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