Molecular Structure of PAN-based Carbon Fiber Precursor

Abstract

The molecular structure of the Polyacrylonitrile(PAN) precursor is known to critically affect the microstructure, and consequently properties, of the final carbon fibers (CFs). Despite the importance of PAN-based carbon fibers, molecular modeling has not been attempted on these precursors and the only structural information available is from models proposed based on XRD experiments. We use molecular modeling to predict the molecular structure of spun PAN fiber precursors and their properties. Our goal is to predict low energy, fully relaxed structures and compare the resulting structures with experiments. The first step in the procedure is to generate a family of helical, rod-like isotactic and atactic isolated chain structures by building chains with a fixed torsional angle ranging from 5ï‚° to 175ï‚°. The second step is to pack the individual chains into a simulation cell following a closed-packed hexagonal arrangement and fully relax the cells using isobaric and isotherm molecular dynamics (MD) simulations. We find that chains built using torsional angles between 120ï‚° and 145ï‚° result in the lowest energy structures in the condensed phase. Furthermore, the simulated structure factors showed excellent agreement with experimental data in both peak positions and relative intensities.