Modeling the Time and Temperature Dependence of the oPs Formation Probability in Polystyrene and Its Derivatives

Positron annihilation lifetime spectroscopy measurements of polystyrene and its derivatives have been performed in the temperature range 20-300 K. The ortho-positronium lifetime calculated from the lifetime spectrum analysis is related to the mean free-volume hole size. However, the ortho-positronium yield in the me- dium is dependent on the polymer chemistry and also on the irradiation effect induced by the positron source. We proposed a model based on two simple processes that cause, respectively, enhancement and inhibition of positronium formation to fit the experimental data over a broad temperature range. Using this model, intrinsic parameters for the polymers under study, such as the shallowly trapped electron recombination energy and the free-radical recombination energy, were calculated and discussed. V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2063-2073, 2009