Unraveling the Rheological Properties of PAN Solutions with Different Solvents (DMAc, DMF, DMSO) and the Morphology of Resulting Nascent Fibers

This study investigated the effects of solvent type (DMAc, DMF, DMSO) and PAN concentration (14–20 wt%) on the viscosity, viscoelasticity, homogeneity of PAN solutions, and the morphology of PAN nascent fibers. Rheological analysis confirmed shear-thinning behavior for all PAN solutions, with distinct differences among the systems. The PAN/DMSO solution exhibited the highest zero-shear viscosity (η0), the lowest flow index (n), and the smallest loss factor (tan δ), indicating the strongest chain entanglement and the highest solution stability. In contrast, the PAN/DMF solution showed the lowest η0, the highest n and tan δ, while the PAN/DMAc system displayed intermediate values. Solution homogeneity decreased with increasing PAN concentration, with the rate of decline following the order: PAN/DMSO < PAN/DMF < PAN/DMAc. Morphological and pore-structure analyses of PAN nascent fibers revealed that solvent selection critically determined the final fiber architecture: PAN/DMSO produced fibers with a compact structure, high porosity, high specific surface area, and predominantly fine pores; PAN/DMAc yielded fibers with moderate porosity and a broad, larger-pore-dominated size distribution; and PAN/DMF led to a denser structure with low porosity, low specific surface area, and a macro-porous architecture. These microstructural variations directly correlated with the rheological properties of the corresponding PAN solution.