Rheological properties and percolation in suspensions of multiwalled carbon nanotubes in polycarbonate

This paper is concerned with several issues related to the rheological behavior of polycarbonate/ multiwalled carbon nanotube nanocomposites. The composites were prepared by diluting a masterbatch of 15 wt.% nanotubes using melt-mixing method, and the dispersion was analyzed by SEM, TEM, and AFM techniques. To understand the percolated structure, the nanocomposites were characterized via a set of rheological, electrical, and thermal conductivity measurements. The rheological measurements revealed that the structure and properties were temperature dependent; the percolation threshold was significantly lower at higher temperature suggesting stronger nanotube interactions. The nanotube networks were also sensitive to the steady shear deformation particularly at high temperature. Following preshearing, the elastic modulus decreased markedly suggesting that the nanotubes became more rigid. These results were analyzed using simple models for suspensions of rod-like particles. Finally, the rheological, electrical, and thermal conductivity percolation thresholds were compared. As expected, the rheological threshold was smaller than the thermal and electrical threshold.Peer reviewed: YesNRC publication: Ye

Observation of Gas Bubble Incorporation during Micropulling-Down Growth of Sapphire

International audienceQuite often sapphire shaped crystals contain specific defects called bubbles of average diameter higher than 100 mu m or microbubbles of diameter smaller than 10 mu m. These defects strongly affect the crystal properties. Bubbles of 100 mu m in diameter have been observed in the molten zone during micropulling-down of sapphire fibers. Before their incorporation inside the crystal, they show a periodic oscillation and consequently deform the crystallization interface. These observations are discussed with reference to the available literature