Ion-chains interaction in polymers

Irradiation of polymeric chains with high energy (10 keV/amu-1.0 MeV/amu) ions gives rise to a complexity of phenomena related to the high value of energy deposited by the ion beams into electronic excitation and/or ionization processes. Typical ion-chain interaction involves crosslinks and scissions formation, which deeply affects the macromolecular structure. The molecular weight distribution of polystyrene suffers a continuous change with ion fluence until the sol-gel transition occurs. A statistical gel-theory allows to correlate these changes to the number of crosslinks per chains produced by ion irradiation. Moreover the modifications in the chemical and morphological properties can be explained on the basis of the gel formation. In semicrystalline polymer (as polyvinylidene fluoride, polyethylene terephatalate and poly paraphenylene sulfide) the crosslinks formation is responsible of the change in the crystallite morphology: the lamellar structure is damaged up to a complete amorphization of the material. The electronic energy loss (S-e) is not a good parameter to explain most of the effects induced in a polymer by high energy irradiation, however they are related to the local energy density in the core track, showing that the lateral distribution of energy deposition influences the polymer modifications. Correlation between the microscopic energy distribution around the ion track and the macroscopic chain modifications will be discussed.