Ion-beam-induced aggregation in polystyrene: The influence of the molecular parameters

Abstract

The formation of an insoluble gel under ion-beam bombardment is governed by ion-beam parameters and target parameters. Here reported is a study of the influence of the target molecular parameters on the sol–gel transition of ion-bombarded polystyrene with particular emphasis for the number-average molecular weight $\overline M$_n. It is shown that the main parameter is the number of macromolecules of the film so that by adopting a “corrected” fluence F/n (ions per macromolecule), the different curves of the various polymers collapse in only one universal curve. The importance of the “corrected” fluence is shown also at molecular level and the MWD of the various polymers is similar at equal F/n values. An experimental model is outlined which explains the sol–gel transition on the basis of transition from an isolated-track regime to an overlap regime where the formation of insoluble giant macromolecules occurs.