Structure development and texture formation in carbonaceous mesophase fibers

Abstract

This paper studied the thermal relaxation phenomena after melt-extrusion of a rigid discotic uniaxial nematic mesophase pitch using mathematical modeling and computer simulation. The Ericksen and Landau–de Gennes continuum theories were used to investigate the structure development and texture formation across mesophase pitch based carbon fibers. It was found that during the thermal relaxation after the cessation of extensional flow the discotic nematic molecules stored elastic free energy decays. The distorted nematic molecules reorient to release the stored elastic free energy. The difference in time scales for molecular reorientation and thermal relaxation resulted in different transverse textures. The rate at which the fibers are cooled is the main factor in controlling the texture development. A slow cooling rate would permit the nematic discotic molecules to reorient to a well developed texture. The random texture is a result of rapid quenching. The numerical results are cconsistent with published experimental observations.