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.
LIPEX ENGINEERING has finalised contract talks with Chinese company to deliver a Nonwoven Tissue Line for basalt fibres. Delivery of the line will be during 2019 and the start-up of the line is planned for first half of 2020.
Near Glendale, California, sits a brand new multi-story housing complex which blends outdoor living with industrial style. The complex provides studio, one-, two-, and three-bedroom floorplans to those interested in urban living.
Holland Composites has been selected to speak at the 2019 Composites in Construction Conference this year in Amsterdam, Netherlands.