Morphological behavior of oxy-PAN fiber upon pH variation

Oxidized-polyacrylonitrile (oxy-PAN) was prepared by oxidation of PAN fiber at 240°C, followed by base catalyzed hydrolysis reaction. The chemical structure of PAN fiber in various pH conditions was characterized by ¹³C-NMR spectroscopy. The characteristic contraction and expansion behavior of oxy-PAN fiber was observed in acidic and basic medium, respectively. In basic condition, water molecules might be absorbed into the fiber with the movement of charge balancing Na ⁺ ion, on the other hand, the water molecules seemed to be expelled in acidic condition to result in contraction. It was also observed that the facile chemical modification occurred due to free diffusion of aqueous reagent into the hydrophilic PAN fiber, and the morphology was affected by pH condition.