Positron Lifetime Study on Microstructural Changes in Iodine-Doped Polymer PPO

Positron lifetime measurements are made in iodine doped (0.2 wt%) poly(2,6-Dimethyl-l,4-Phenylene Oxide) films under an isochronal annealing cycle in the temperature range 25 to 200 °C. The measured lifetime spectra are best fitted to three component analysis. The annihilation parameters as a function of isochronal annealing temperature show some interesting microstructural changes. The average free volume size at each temperature is calculated from the ortho-positronium lifetime using an equation of Nakanishi based on a theoretical model of Tao. The variation of lifetime parameters as a function of isochronal annealing temperature seems to suggest that there is a structural relaxation process in the temperature range 25 to 70 °C which may be due to different types of rotations and oscillations of the methyl group present in the polymer. The ortho-positronium yield increases in the range 55 to 160 °C indicating the increase in the electron mobility. Comparision of lifetime parameters of undoped and doped states of the polymer indicates that the iodine dopant diffuses mostly into the disordered micro regions of the polymer.