Ramanan Krishnamoorti has been working on nanotechnology since before the funding boom, years before President Bush signed the National Nanotechnology Initiative in 2003 allocating $3.7 billion in federal support.

Today his research is establishing the governing principles that will lead to lighter, safer and more durable cars and airplanes, and it holds promise for other groundbreaking improvements in polymer-based products.

“I started here in 1996, and since then we’ve been working on what are called polymer nanocomposites, and the idea is to disperse nanoparticles of various kinds in to polymeric matrices,” says Krishnamoorti, UH professor of chemical engineering. The underlying goal of his research is to radically improve products made of plastic, rubber, nylon and other such materials by strategically adding carbon nanotubes or layered silicates during processing. Carbon nanotubes are cylindrical-shaped molecules with exceptional properties of strength, toughness, stiffness, and electrical and thermal conductivity.

Why would you want to do something like that? People have long been putting macroscopic fillers like carbon black and glass fibers or talc into polymers to reinforce them, to simply make the materials stronger. The downside of those traditional fillers is they increase the weight of the polymers by 40 to 50 percent. By contrast, Krishnamoorti’s nanoparticles typically increase the weight by 0.1 to 5 percent, and the benefits in mechanical properties far surpass those achieved by the use of traditional fillers.

Krishnamoorti’s work with nanocomposites received a major boost in 1999 when he was awarded a prestigious CAREER grant from the National Science Foundation. Today, his work is funded by a multitude of public and private entities, including ExxonMobil, which funds work on layered silicates, and NASA Langley, which provides funds through its University Research and Engineering Technology Institutes (URETI). The purpose of URETI is to research and exploit innovative and emerging opportunities in technology that can have a revolutionary impact on the missions NASA pursues in the future.

The stunning success of nanocomposites over traditional fillers provides a clear illustration of the kind of improvements that can be realized by the application of Krishnamoorti’s discoveries in commercial products.

“Our approach uses nanoparticles, which are comparable in weight to many of these macroscopic fillers, but we use an order of magnitude lower amount of it and the benefits are exponentially greater,” says Krishnamoorti, who holds a Ph.D. in chemical engineering from Princeton University. “The idea is, I can use very small amounts of very expensive nanotubes in a very cheap polymer, keep the cost down and have synergistic properties that you could never achieve before at those kinds of loadings. I’ve essentially not altered the density of the material. We exploit the fact that nanotubes have a very high surface area-to-volume ratio, which affects the way they connect to the polymer.”

Why does the surface area matter so much?

“If I put a large surface area there, then by interaction with that surface, the polymer gets reinforced,” he says. “You don’t need to get covalent chemical bonding to get stress transfer. All you need is intimate mixing and attraction between the polymer and the nanotubes. We’ve done this with a variety of materials and we have several patents that are being issued right now.”

One such application is in automobiles.

“We’re trying to lightweight automobiles,” Krishnamoorti says. “For instance, gas tanks are made of polyethylene, and one of the problems with these materials is they do let some of the gasoline out through the polyethylene into the air. We use layered silicates—nanometer-thick materials, disk-like objects that have basically the aspect ratio of a sheet of paper—to serve as a barrier within the polyethylene. The silicate is very thin but very large in lateral size. It can be half a micron in diameter but one nanometer in thickness. We disperse it within the polymer, and these silicates, because they are hard ceramic materials, will not let a gas pass through them. Instead, it must go around. Essentially, we increase the path dramatically by which the molecule has to traverse to get out into the air.”

Krishnamoorti has several patents pending in the area of nanotubes. His research group takes naturally clustered nanotubes, unclusters them and then disperses them in the polymer. His group holds the record for the lowest dispersion of nanotubes in polymers.

Cynthia Mitchell (2005 PhD ChE) works on an ultraviolet-visible-near infra red absorption spectrometer in professor Ramanan Krishnamoorti’s lab.

“There are three ways of trying to achieve efficient dispersion of nanotubes in polymers,” explains Krishnamoorti. “One is by doing chemical functionalization. The second is to put the nanotubes in some kind polymerizable monomer: You do an in-situ polymerization, just a physical mixing. The third way is surfactant-assisted. You take soap-like molecules in a very small amount, and they act as a compatibilizing agent.”

The Holy Grail of nanotube research, according to Krishnamoorti, is discovering how to extend this process to the polymers of commercial interest that are produced in large amounts, and to achieve these desired properties with low concentrations of nanotubes. Low concentrations are important because nanotubes are very expensive as additives.

“We’re trying to move into commodity materials—like polyolefins,” Krishnamoorti says. “The other thing that we’re working on is high-temperature polymers. We’re just starting a collaborative process with the Air Force.”

Krishnamoorti says the lowest hanging fruit in his research is the area of reinforcing elastomers, basically rubber-based materials. This has very wide-ranging applications, from down-hole oil well drilling to NASA, which is looking for sealants. Elastomers by nature are rather soft, pliant material. Krishnamoorti’s group is finding ways to improve their strength while keeping the most important aspect, their elastic properties.

“We tune the material chemistry to try and tune the materials physics and at the same time, what set our group apart from perhaps most of what people do in the nano business is we try to incorporate processing as an integral step of trying to understand structure-property relations,” Krishnamoorti says. “Because in all of these nanomaterials, processing is the crucial aspect. You can control structure more by processing than by, even chemistry, for example. As long as you have favorable chemistry, you can get any structure you want and you can trap it in that structure and get the enhanced properties by processing. And that’s the most important angle that we bring to bear. It addresses a very important disconnect that happens in academic and industrial research.”

What is processing exactly? Examples might include sending plastic through an extruder, an injection molder, a blow molder, or a sheeting apparatus. Processing might also include subjecting the material to high temperature, high pressure and flow, meaning shear or elongation. Many of these steps may also be applied during cooling, which will solidify the material and further effect the final properties of the material.

Krishnamoorti wants to be able to say how each of these processes affects the structure and the properties of the material. For traditional polymer materials, the governing principles are quite well established, both at the scientific level and at the industrial level. But the area where much less is known is the area of nanocomposites. The idea is to try to come up with governing principles so that new products with remarkable new properties can be developed.