Formation and structure of iodine complex of polyacrylonitrile studied by vibrational spectroscopy

It has been reported that polyacrylonitrile (PAN) can form a complex with polyiodide ions, which can give some interesting thermal and electronic properties to PAN. However, the formation process and structure characteristics of the PAN-iodine complex interpreted from the molecular level are still unclear. The present research is devoted to clarifying the above problems by studying the PAN film immersed in the iodine aqueous solution with different concentrations and counter cations based on IR and Raman spectroscopy in detail. We have found that the PAN-iodine complex can form through the intermolecular interaction between PAN chains and I5− ions by immersing the PAN film into the iodine aqueous solution with an iodine concentration higher than 0.1 mol/L. The ν(CN) and δ(CH2) modes in the IR spectra of PAN showed a remarkable shift through forming the complex in the 1 mol/L iodine solution. Moreover, the PAN-iodine complex formed in the iodine solutions containing the different types of counter ions (K+, Na+, Li+) may have different structures based on different band positions of ν(CN), δ(CH2), and ν(CH2) mode in their IR spectra. More interestingly, we found that during the formation of the complex, the content of planer zigzag conformation along the atactic PAN chain increased obviously. The present study results may inspire to further develop PAN as a functional polymer material.