The orientational behavior of multiwall carbon nanotubes in polycarbonate in simple shear flow

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.     

General Uniqueness Results and Variation Speed for Blow-Up Solutions of Elliptic Equations

Let be a smooth bounded domain in R^N. We prove general uniquenessresults for equations of the form – u = au – b(x)f(u) in , subject to u = on . Our uniqueness theorem is establishedin a setting involving Karamata's theory on regularly varyingfunctions, which is used to relate the blow-up behavior of u(x)with f(u) and b(x), where b 0 on and a certain ratio involvingb is bounded near . A key step in our proof of uniqueness usesa modification of an iteration technique due to Safonov. 2000Mathematics Subject Classification 35J25 (primary), 35B40, 35J60(secondary).