Molecular insights into the initial formation of pyrolytic carbon upon carbon fiber surface

Understanding the deposition process of pyrolytic carbon is essential in controlling its microstructure and consequent macroscale performance. Herein, using molecule dynamics (MD) simulations with the ReaxFF potential, we revealed the initial formation process of pyrolytic carbon near the simplified surface of carbon fiber. Three stages were identified in the deposition process, where polycyclic aromatic hydrocarbons (PAHs) formed from precursor gas at first, followed by the deposition and assembly process of PAHs and subsequently the continuous chemisorption of light carbon species. The impacts of temperature, gas density and surface defects were investigated separately. Our results suggest that PAHs would be the main source of the deposition under high gas density and surface defects would promote the deposition prominently. Comparing formed pyrolytic carbon structures under different conditions, we also found that PAHs would produce more defects and interlayer connections while the growth from light carbon species would achieve a more intact in-plane architecture. Moreover, the potential relations between our simulated structures and previous experimental observations were discussed to explore the initial formation mechanism of pyrolytic carbon in actual deposition process. The MD simulation data and insights obtained here might be significant for understanding the deposition process of pyrolytic carbon at atomistic scale. (C) 2019 Elsevier Ltd. All rights reserved.