The orientational behavior of multiwall carbon nanotubes in polycarbonate in simple shear flow |
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Authors: | Dirk J Dijkstra M Cirstea N Nakamura |
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Institution: | (1) Bayer Material Science, CAS-INN-Physics, 51368 Leverkusen, Germany;(2) Department of Materials, University of Oxford, Oxford, OX1 3PH, UK;(3) Department of Chemical Engineering, Kyoto University, Kyoto 615-8510, Japan |
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Abstract: | This paper describes the changes in the orientation of multiwall carbon nanotubes (MWCNT) in polycarbonate as determined by
transient and oscillatory shear rheology. It is well known from rheological studies on composites with macroscopic fibers
that the overshoot in transient shear viscosity is caused by the change in orientation distribution of these fibers. This
study shows that although an overshoot in transient shear viscosity of MWCNT/polycarbonate is measured at shear rates as low
as 0.1 s − 1, the MWCNT network is disturbed only at considerably higher shear rates. Scanning electron microscopy micrographs and oscillatory
shear show that MWCNT in thermoplastic composites will only be oriented at high shear rates. Simultaneous measurements of
the electrical conductivity during rheological start-up shear and oscillatory measurements show large differences between
electrical and mechanical relaxation behaviors. The viscosity of the composite seems to depend strongly on the MWCNT network
density, whereas the proximity of the tubes at the network points seems to determine the electrical properties of the MWCNT
composite. |
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