Ion-beam effects on optical and rheological properties of polystyrene

Ion-beam irradiation induces large changes in optical and rheological properties of polystyrene films. High-energy (100–300 keV) ion irradiations in the fluence range ${10}^{11}$–5×${10}^{14}$ ions/${\mathrm{cm}}^2$ produces optical defects in the original polymer chains (MW=9000 amu). A linear dependence on ion fluence has been detected up to a defect density of 2×${10}^{20}$ def/${\mathrm{cm}}^3$. Defect production rate depends on the energy loss of incoming ions and the chemical yield (bonds/100 eV) increases from 0.07 to 0.28 going from an energy loss of 10 eV/Å to 20 eV/Å, being the difference related to the spatial energy distribution inside the ion track. Rheological behavior, as solubility and molecular weight distribution, is modified after irradiation because the formation of cross-links between the main chains. The cross-link density exhibits a linear trend at low fluence (≤${10}^{14}$ ions/${\mathrm{cm}}^2$) and a saturation at high fluence (${10}^{14}$–${10}^{15}$ ions/${\mathrm{cm}}^2$), when an average number of one cross-link per chain is produced. Correlation between optical and rheological data suggests that only optical measurements are correlated to the total bonds produced by ion irradiation in all the fluence range.