Understanding mesophase pitch from a lyotropic liquid crystalline perspective

Abstract

This review explores recent research regarding mesophase pitch (MP). Spinnable mesophase pitch (SMP) was used as a model pitch for MP in all experiments. We explain some phenomenological results of the lyotropic liquid crystalline properties of the SMP, which show that the MP behaves as a typical lyotropic liquid crystal. The mesogenic and solvent components of SMP are defined. We define the threshold concentration (TC) as the minimum amount of mesogenic component necessary for SMP to achieve 100 vol% anisotropy. We also report the TCs of various SMPs and discuss the effects of the solvent component. Concerning the identity of the mesogenic component, we discuss quantitative correlations between the size of the layered molecular stacking units and the anisotropic content of the SMP. Research has shown that a layered molecular stacking unit larger than a specific size corresponds to the mesogenic component of the MP. We discuss a novel method for the manufacture of SMPs using our understanding of MP as a lyotropic liquid crystal, which comprises thermal mixing of optimal amounts of the mesogenic and solvent components that were prepared separately under different conditions. This method enables the properties of each component to be optimized without involving a costly hydrogenation process. Finally, we discuss how this approach can be used to increase SMP yield by modifying the contents of the anisotropic mesogenic and solvent components.