Investigating the structure, dynamics, and phase behaviour of polycyclic aromatic hydrocarbons derived from coal tar pitch: (I) temperature dependence

Abstract

Carbon fiber (CF) is regarded as a “wonder material” in modern era for its several advantageous technological applications. It justifiably boasts of its light weight and high tensile strength. Unfortunately, the increased raw material cost of PAN-based CF restricts the horizon of its applications with an otherwise enormous potential. To this end, coal tar derived pitch is rich in poly aromatic hydrocarbons (PAHs) and can be a cheaper, promising source of precursors for CF manufacturing. Thus, herein, we have performed molecular dynamics (MD) simulation of several coal tar PAHs (varying in molecular weight and aromaticity) at various temperatures with an aim to enrich the current state of understanding on some intriguing precursor behaviours. This leads to the findings that low molecular weight precursors are most suited to form isotropic phase (random arrangement), whereas high molecular weight precursors are best suited to develop mesophase (ordered arrangement). Softening point of the precursors generally elevates with increase in molecular weight, but it is also affected by the phase of the system. The phase transition of pitch precursors from solid to liquid is not abrupt; rather, we discover a temperature range of phase coexistence that broadens as molecular weight increases.