Radiation-induced energy and charge transport in polystyrene - Laser photolysis and pulse radiolysis comparative study

The radiation induced processes in polystyrene films have been studied by laser photolysis and pulse radiolysis using transient spectroscopic techniques. Transport of the singlet excitation in polystyrene was found to be temperature dependent, and the average excitation migration rate constant was estimated to be similar to 5.0x10(11) M(-1)s(-1) at 293 K and 0.5 similar to 1.0x10(11) M(-1)s(-1) at 80 K. The concentration of excimer forming sites in room temperature equilibrated polystyrene was measured to be around 0.1 M by competitive quenching kinetics. Efficient generation of excited states, cation and anion radicals of solutes was observed in electron irradiated polystyrene films, concomitant with the quenching of the polymer singlet excited state. The yields of pyrene transients at [Py]=100 mM were measured: G((1)Py*)similar to 0.6, G((3)py*)similar to 1.0, G(Py(+.))similar to 1.6, and G(Py(-.))similar to 0.8. Fast kinetic measurements resolved the concentration dependent formation rates of solute excited states and cation radicals that was within similar to 2 ns. Migration of the positive hole in the polymer matrix was proposed to account for the production of solute excited states via geminate recombination with solute anions and the generation of solute cations by charge transfer to solutes at encounter. The positive charge migration coefficient was estimated from the bimolecular reaction rate to be Lambda(h) similar to 3x10(-5) cm(2)/s. Simulation of the experimental data shows that the thermalization length of excess electrons is 56 Angstrom in solid polystyrene, and that similar to 70% of the polystyrene excimer is derived from the subsequent geminate ion recombination.