Modeling elastic and viscous effects on the texture of ribbon-shaped carbonaceous mesophase fibers

Abstract

Carbonaceous mesophases are discotic nematic liquid crystals that are spun into high performance carbon fibers using the melt spinning process. The spinning process produces a wide range of different fiber textures and cross-sectional shapes. Circular planar polar (PP), circular planar radial (PR), ribbon planar radial (RPR), and ribbon planar line (RPL) textures are ubiquitous ones. This paper presents, solves, and validates a model of mesophase fiber texture formation based on the classical Landau-de Gennes theory of liquid crystals, adapted here to carbonaceous mesophases. The effects of fiber cross-sectional shape and elongational flow on texture formation are characterized. Emphasis is on qualitative model validation using existing experimental data [1]. The role of elasticity and flow-induced orientation on texture selection mechanism on ribbon-shaped mesophase fibers is characterized. The model is able to predict the formation of the commonly observed line texture, and the fine structure of the line is reproduced and explained in terms of classical liquid crystal defect physics. The results provide additional knowledge on how to optimize and control mesophase fiber textures.