Rheology of carbonaceous mesophase pitch

Abstract

Abstract Limited rheological data on mesophase pitches have begun to appear in the literature only recently. Significant response time after imposition of stress and the strong temperature dependence of apparent viscosity observed in these materials require considerable experimental precaution. Careful attention has been given in this study to possible pitfalls inherent in the measurement of apparent viscosity both in the Couette and the Poiseuille flow modes. A description of the experimental methodology is given. Although the apparent viscosities of some mesophase pitches were invariant over a wide range of shear rate, the same pitches also exhibited the Weissenberg effect and die swell. Consequently, they are somewhat viscoelastic and cannot always be regarded as Newtonian liquids. The activation energy for viscous shear flow in mesophase pitches is similar to that encountered in polymeric materials. The rheological properties often reflect the two-phase composition of mesophase pitches and/or their liquid crystalline nature.