Double-diffusion model for cross-section formation and shape evolution of profiled fibers during coagulation process

Fiber cross-section heterogeneity is beneficial for improving the carbon fiber-composite interaction force and achieving the carbon fiber mechanical enhancement effect. The double-diffusion of the solvent and coagulant in solidification molding is a key factor affecting the morphology and structure of profiled PAN (polyacrylonitrile) fibers, which has not been disclosed well by experiment or simulation. To simulate the path of fiber morphology variation during solidification process which cannot be obtained by traditional model and boundary conditions, a mathematical model was introduced with volume-control parameters that can depict the coupling effect of morphology change from double-diffusion mass transfer process, and revealed the synergistic between the dynamics of morphology path and diffusion coefficient ratio visually. It was found that the diffusion coefficient was the main factor contributing to variation of morphology differences at low drawdown, while the difference in double-diffusion coefficient between the solvent and coagulant promoted development of morphology differences. Finally, the solvent diffusion coefficient was found to be 3.2 × 10⁻¹⁰ m²·s⁻¹, and the closer the ratio of diffusion coefficients tended to 1, the greater the degree of morphological anisotropy of the solidified fibers, the smaller the cross-sectional variability. Selecting typical trilobal fibers as samples, the simulation results of the morphological changes in the solidification process were verified by experiment, which can provide an effective means to study the morphological regulation of functionalized heterogeneous fibers.