The rheological behaviors of polyacrylonitrile (PAN) and its copolymers in various NaSCN aqueous solutions are investigated. An unusual shear-viscosity behavior that is unique for PAN/NaSCN aqueous solutions is identified: both in the high and low NaSCN concentration (C-NascN) regimes, the PAN solution viscosities are higher, with the minimum occurring at C-NascN = 48-50 wt% for the 11wt% PAN solutions. Infrared spectroscopic and dynamic light scattering measurements are employed to elucidate the solution-structural changes that are responsible for this unusual viscosity behavior. Accordingly, a tentative dissolution mechanism in PAN solutions with high C-NaSCN and gelation mechanism with low C-NaSCN are proposed. (C) 2015 Published by Elsevier Ltd.