Research Multi-Scale Modeling

Putting Nanotubes to Work

Carbon nanotubes are mocroscopic structures composed of graphite-like carbon rolled into hollow tubes with diameters on the order of one nanometer. These nanotubes have remarkable electronic and mechanical properties, as shown by experiment and theoretical calculations. The unique properties of nanotubes make them promising candidates for a variety of applications, such as single-molecule transistors, nanowires, chemical sensors, novel catalytic supports, components in nano-engineered machines, fibers for nanocomposite materials, and molecular sieves for gas storage and separations.

Professor Johnson is investigation the properties of carbon nanotubes and exploring their usefulness through molecular simulation and electronic structure calculations. He is currently working on chemical and physical storage of hydrogen on idealized and more realistic models of nanotubes. His interests also include gas separations, quantum confinement, chemical reactions inside nanotubes, metal-nanotube interactions, the effect of defect sites on the electronic properties of nanotubes, and the use of nanotubes in catalysis.

Discrete Modeling of Particular Systems

Discrete Modeling of
Particular Systems

Granular materials exhibit a vast array of unusual phenomena—spontaneous segregation, pattern formation, etc,—and have been a traditional bottleneck in numerous industries. A primary cause of much of their unique behavior can be traced to the nature of particle-particle interactions, which introduce new forces and length scales which may create difficulty for continuum modeling of these systems.

New discrete, multi-physic, modeling tools developed in Professor McCarthy's group show promise for bridging the gape between the micro-scale (particle-scale) and the meso-scale (pilot-scale).

Using these tools, they find that the ubiquitous contact and stress heterogeneities in particulate systems—caused by stress "chains"—may serve as the nucleus of hot spots in solid-catalyzed reactors or stored granular material. Also, recent work has been done that calls into question the old adage that cohesion limits segregation.

Pitt Researchers Create Large-scale Networks with Nanoscale Rods Advances in Microelectronics, Super-strong Polymers Possible

Adding solid rods measuring just a few billionths of a meter long to polymers can dramatically improve the mechanical, thermal, and electrical properties of the mixture. Research by Professor Balazs in collaboration with Professor Jasnow, of Pitt's physics and astronomy department, used two-dimensional simulations to examine how the tiny rods interacted in mixtures of two polymers.

Their findings could lead to faster and easier production of electrically conducting pathways in insulating materials or to the creation of reinforcing structures in organic/inorganic compolites. The researchers found that nanotubes embedded in the polymers that naturally repel one another can align end-to-end, creating possible electrical pathways in the mixture. Rod-like nanoparticles naturally arrange themselves into percolating networks that strengthen the polymer blend to which they are added.

"The rods themselves are small—a few billionths of a meter—but the networks extend throughout the material," said Balazs. The individual rods are on the nanometer scale, but self-assembled into the network, they extend throughout the material. In that sense, they are very large.

These findings should assist in developing new materials. Most promising, say Balazs and Jasnow, are applications in the automotive industry, where the electrical pathways created by nanotubes could be used to create more efficient batters, and strong polymers could be fabricated into lightweight parts for automobile bodies and chassis.

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