Free-volume of polycarbonates at different gas pressure studied by positron annihilation

Positron lifetime measurements have been carried out to investigate the free volume hole sizes in a series of polycarbonates at different gas concentrations. Argon and CO2 were used to occupy the larger holes of the free volume. The formation of positronium (Ps) offers the possibility to investigate the non-occupied sites of the free-volume using a semiempirical approach of Jean [1,2] for a correlation between the average Ps-lifetime and the average free-volume size. Using a model of a gaussian distribution of the volume sites [3,4] one can determine the changes in the average size of the sites and the number density of free-volume sites in the polymer. At higher concentrations swelling of the polymer occurs and the microstructure changes with incomplete reversibility.