Positronium as a probe of sorption mechanism in polytetrafluoroethylene

As one of the series of works of application of positron annihilation technique to the study of sorption of polymers, sorption of CO2 and CH4 into polytetrafluoroethylene has been measured. The lifetimes of the two o-Ps states, τ3=1.6 ns and τ4=4 ns in vacuum, were increased with the charged gas pressure. The intensity of the longer lived component, I4, was decreased showing that the sorbed molecules and o-Ps are competing for the free volume sites in the amorphous parts. The intensity of the shorter lived component, I3, did not decrease substantially. From these results it is concluded that the τ3 component corresponds to o-Ps annihilating in the interphase region between the crystalline and amorphous parts. It has also been deduced from the results that positronium increases the size of the holes.