SOLVENT-INDUCED TRACK SENSITIZATION - EXTRACTION OF OLIGOMERS

Oligomer extraction from polyethylene terephthalate (PET) irradiated by xenon ions of 11.4 MeV/u is investigated using UV spectrophotometry and gel permeation chromatography (GPC). The cyclic trimer is identified as the predominant diffusing species removed during extraction by dimethyl formamide (DMF). Extraction dynamics is modeled by a rapid (time constant almost-equal-to 2 min) and a slow (time constant almost-equal-to 100 min) diffusion process attributed to the latent ion tracks and to the virgin material, respectively. Thereby latent tracks act simultaneously as irrigation and drainage pipes for the transfer of the solvent into and the extraction of oligomers from the polymer matrix. Thus tracks help to release osmotic pressure differences and to avoid blistering of the unirradiated polymer during solvent exchange. The total extracted mass per track shows a characteristic decrease with increasing ion fluence interpreted as oxygen effect, due to the decreasing supply of oxygen in the sample during irradiation. The extractable mass corresponds to an equivalent track diameter of initially around 10 nm contracting with increasing ion fluence to an asymptotic value around 3 nm.