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.
ZSK will hold its bi-annual technology showcase on 21-22 September 2018 at its Krefeld, Germany, headquarters. The Embroidery Technology Show assembles more than 25 exhibitors from around the world to discuss emerging trends in the embroidery manufacturing industry and demonstrate the latest products produced using techniques such as tailored fibre placement (TFP) or smart textiles.
Fibrelite reports that since the start of its partnership with Trenwa more than 100 precast trench systems integrating Fibrelite composite covers have been sold for use in electrical substations, wastewater treatment plants, chemical refineries and many other applications across North America.
Parth Rawal, a scientist at the Fraunhofer Institute for Manufacturing Technology and Applied Materials (IFAM), Stade, Germany, has been presented with the MT Aerospace Innovation Award for his master thesis Sensor Based Online Monitoring System for Detection of Milling Defects on CFRP Structures.