11 February 2008
11 February 2008
New measurements by scientists at the National Institute of Standards and Technology (NIST) show that the electrical properties of a composite can be tuned from being a conductor to a non-conductor simply by changing processing conditions..
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.
* 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.
LANXESS will open a new applications development and technical services (AD & TS) laboratory for polyurethane dispersions (PUDs) in Latina, Italy. This will be capable of supporting market needs in a variety of coatings and adhesives applications in leather and textile finishing, plastic, glass and metal substrates coatings, as well as glass fibre sizing.
Applications for composites in the sports and leisure sector will be showcased by various exhibitors at Composites Europe in Stuttgart, Germany, on 6-8 November.
The Massachusetts Department of Transportation (MassDOT) selected a lightweight FiberSPAN fibre reinforced polymer (FRP) bridge deck, manufactured by Composite Advantage, for the Rugg Bridge on Route 57.