Rheologica Acta

, Volume 49, Issue 8, pp 845–854

Rheostructural studies of a discotic mesophase pitch at processing flow conditions

Original Contribution

DOI: 10.1007/s00397-010-0448-7

Cite this article as:
Kundu, S. & Ogale, A.A. Rheol Acta (2010) 49: 845. doi:10.1007/s00397-010-0448-7

Abstract

The flow-induced microstructure of a mesophase pitch was studied within custom-made dies for changing wall shear rates from 20 to 1,100 s − 1, a flow scenario that is typically encountered during fiber spinning. The apparent viscosity values, measured at the nominal wall shear rates ranging from 500 to 2,500 s − 1 using these dies, remain fairly constant. The microstructure was studied in two orthogonal sections: rθ (cross section) and rz (longitudinal mid plane). In these dies, the size of the microstructure gradually decreases toward the wall (to as low as a few micrometers), where shear rate is highest. Furthermore, as observed in the rθ plane of the capillary, for a significant fraction of the cross section, discotic mesophase has a radial orientation. Thus, the directors of disc-like molecules were aligned in the vorticity (θ) direction. As confirmed from the microstructure in the rz plane, most of the discotic molecules remain nominally in the flow plane. Orientation of the pitch molecules in the shear flow conditions is consistent with that observed in controlled low-shear rheometric experiments reported earlier. Microstructral investigation suggests that the radial orientation of carbon fibers obtained from a mesophase pitch originates during flow of pitch through the die.

Keywords

Mesophase pitchDiscotic liquid crystalsMicrostructureOrientation

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Department of Chemical and Biomolecular Engineering, Center for Advanced Engineering Fibers and FilmsClemson UniversityClemsonUSA
  2. 2.National Institute of Standards and TechnologyGaithersburgUSA