New measurements by scientists at the National Institute of Standards and Technology (NIST) have uncovered an intriguing wrinkle. For a given CNT concentration, the electrical properties of the composite can be tuned from being a conductor to a non-conductor simply by changing processing conditions—basically how fast the polymer flows.
Carbon nanotubes—sheets of graphite rolled up into nanoscale hollow cylinders—are under intense scrutiny for a wide range of materials applications. The NIST study shows how the conductivity and dielectric properties of these mixtures depend on flow and how they change once flow has stopped. These property changes have relevance to the process design of these materials in a long list of potential applications for conducting plastics including transparent electrodes, antennas, electronic packaging, sensors, automotive paint, anti-static fuel hoses and aircraft components.
The NIST researchers augmented a standard instrument, a shear rheometer, normally used for viscosity measurements, to simultaneously measure conductivity and dielectric properties Using this “rheo-dielectric spectrometer,” they discovered that the conductivity of the nanocomposite dramatically decreases with increasing flow rate, effectively changing the material from a conductor to an insulator.
This extraordinary sensitivity of the conductivity (and other properties) to flow is prevalent near a characteristic CNT concentration where an interpenetrating CNT network first forms. Surprisingly, once the flow is removed, they found that the nanocomposite reverts back to its original conductivity.
Based on these measurements, the NIST team proposed a theoretical model that successfully accounts for these dramatic effects. This model quantitatively predicts the observed conductor-insulator transition and is useful for optimizing and controlling the properties of these new polymer-nanotube composites.
Citation: J. Obrzut, J.F. Douglas, S.B. Kharchenko and K. B. Migler. Shear-induced conductor-insulator transition in melt-mixed polypropylene-carbon nanotube dispersions. Physical Review B 76, 195420-2007. Nov. 15, 2007.
Source: NIST
Related stories:
NIST WTC 7 Investigation Finds Building Fires Caused Collapse
The fall of the 47-story World Trade Center building 7 (WTC 7) in New York City late in the afternoon of Sept. 11, 2001, was primarily due to fires, the Commerce Department’s National Institute of Standards and Technology (NIST) announced today following an extensive, three-year scientific and technical building and fire safety investigation. This was the first known instance of fire causing the total collapse of a tall building, the agency stated as it released for public comment its WTC investigation report and 13 recommendations for improving building and fire safety.
Nanoparticle Research Points to Energy Savings
(PhysOrg.com) -- Adding just the right dash of nanoparticles to standard mixes of lubricants and refrigerants could yield the equivalent of an energy-saving chill pill for factories, hospitals, ships, and others with large cooling systems, suggest the latest results from National Institute of Standards and Technology research that is pursuing promising formulations.
‘Electron Trapping’ May Impact Future Microelectronics Measurements
Using an ultra-fast method of measuring how a transistor switches from the “off” to the “on” state, researchers at the National Institute of Standards and Technology (NIST) recently reported that they have uncovered an unusual phenomenon that may impact how manufacturers estimate the lifetime of future nanoscale electronics.
NIST reference materials are 'gold standard' for bio-nanotech research
The National Institute of Standards and Technology has issued its first reference standards for nanoscale particles targeted for the biomedical research community—literally “gold standards” for labs studying the biological effects of nanoparticles. The three new materials, gold spheres nominally 10, 30 and 60 nanometers in diameter, were developed in cooperation with the National Cancer Institute’s Nanotechnology Characterization Laboratory (NCL).
‘High Q’ Nanowires May be Practical Oscillators
Nanowires grown at the National Institute of Standards and Technology (NIST) have a mechanical “quality factor” at least 10 times higher than reported values for other nanoscale devices such as carbon nanotubes, and comparable to that of commercial quartz crystals. Because a high Q factor indicates a capacity for stable vibrations, the nanowires might be used as oscillators in nano-electromechanical systems for future nano-sensors and communications devices.
NASA Goddard Space Flight Center's carbon nanotube manufacturing technology wins Nano 50 Award
NASA Goddard Space Flight Center in Greenbelt, Md. announced that its method for manufacturing high-quality carbon nanotubes (CNT) has been named a winner in the third annual Nanotech Briefs Nano 50 awards in the Technology category. This award will be celebrated at the Nano 50 awards dinner November 14 at the NASA Tech Briefs National Nano Engineering Conference (NNEC 2007) in Boston, Mass.
Helping the carbon nanotube industry avoid mega-mistakes of the past
A new analysis of by-products discharged to the environment during production of carbon nanotubes (CNTs) — expected to become the basis of multibillion-dollar industries in the 21
st Century — has identified cancer-causing compounds, air pollutants, and other substances of concern, researchers reported here today at the 234
th national meeting of the American Chemical Society.
Penn Physicists Develop a Carbon Nanotube Aeroegel Optimizing Strength, Shape and Conductivity
Researchers at the University of Pennsylvania have created low-density aerogels made from carbon nanotubes, CNTs, that are capable of supporting 8,000 times their own weight. The new material also combines the strength and ultra-light, heat-insulating properties of aerogels with the electrical conductivity of nanotubes.
