• A novel method combining atomic force microscopy (AFM), 2D Fast Fourier Transform (2D FFT), and inverse FFT (iFFT) is developed to quantify hierarchical surface grooves on carbon fibers and their precursors. • The evolution of multi-scale grooves is tracked across six key process stages, revealing an interplay of competing mechanisms including: phase separation, axial drawing, and radial shrinkage. • Quantified groove evolution serves as a powerful indicator, directly indicating the final tensile strength of carbon fibers. • The methodology provides a robust framework for process monitoring and quality control, enabling the optimization of high-performance carbon fiber production. Surface defects, particularly longitudinal grooves, significantly limit the mechanical performance of carbon fibers (CFs). While these defects are often inherited from precursor fibers, quantitatively tracing their multi-scale evolution throughout the manufacturing process remains a critical challenge. Here, we present a novel, non-invasive analytical methodology combining atomic force microscopy (AFM) with two-dimensional Fast Fourier Transform (2D FFT) and inverse FFT (iFFT) reconstruction. This methodology resolves the complex surface topography of PAN-based fibers into three hierarchical levels, each attributable to the specific physical origins: microfibril stacking, fibril aggregation, and surface wrinkling. We successfully traced the evolution of these hierarchical groove structures through six key process stages, from coagulation to carbonization. This analysis revealed that groove evolution is dictated by a complex interplay of phase separation, axial drawing, and radial shrinkage, and the dominant mechanism varies at different stages. Most importantly, we established a direct correlation between the surface defects of the precursor fiber and the final mechanical performance of the carbon fiber. Our method precisely quantified how process-induced instability, marked by a dramatic deepening of grooves in early stages, directly compromises final fiber strength. Therefore, this work not only provides a powerful characterization technique but also serves as an invaluable tool for process monitoring and quality prediction, offering a new quantitative pathway to optimize the production of high-performance carbon fibers. For Table of Contents use only.
Lu et al. (Fri,) studied this question.