Monte Carlo study of molecular weight distribution changes induced by degradation of ion beam irradiated polymers

V.C. CHAPPA; C. PASTORINO; M. F. DEL GROSSO; C. R. ARBEITMAN; M. MÜLLER; G. GARCIA BERMUDEZ

Padova, Italia

Simposio; Radiation Effects in Insulators REI 2009; 2009

Universidad de Padova y Universidad de Venecia

In this work we study the changes in molecular weight distribution of a polymeric material that degrades uponirradiation due to the inhomogeneous energy deposited by heavy ion beams.Ion beam irradiation of polymers generates rather different effects than those induced by “classical” low ionizingparticles e.g., electrons or gamma rays. This is due to the high electronic stopping power and the inhomogeneousdistribution of deposited energy. This energy is transferred to the material within a small volume along the ion pathforming the so called “nuclear track” or “latent track”. The track size primarily depends on the ion velocity, and it isdetermined by the secondary electrons (delta rays) generated along the ion trajectory. By means of a Monte Carlosimulation we first obtained equilibrated polymer configurations using a coarse-grained model, and then investigatedthe spatially inhomogeneous chain scission process due to the passage of the ions. The number average molecularweight, weight average molecular weight and the polydispersity were calculated as a function of track radius,probability of scission within the ion track and fluence of the ion beam. Finally we compared our results with anintegro-differential model by Saito based on different assumptions such as, e.g., random homogeneous polymerdegradation.