Positron lifetime study of the free-volume properties in the polymer polyacrylonitrile

Positron lifetime measurements have been made in the polymer polyacrylonitrile, in the iodine doped state as well as the undoped state. The measured lifetime spectra were well resolved into three components. The behaviour of the intermediate component and its intensity seems to indicate an initial positron trapping at the interfaces between the amorphous and the crystalline regions and a later trapping by the kinks of the crystalline region. From the behaviour of the average free-volume size and its density we interpret that the iodine atoms initially occupy the free-volume sites in the amorphous region and at larger concentrations they form complexes with the nitrile group of the polymer