Influence of implantation of heavy metallic ions on the mechanical properties of two polymers, polystyrene and polyethylene terephthalate

Ion implantation of polyethylene terephthalate (PET) and polystyrene (PS) with various high energy metallic ions at 70 kV and a dose of 3 × 10¹⁶ ions/cm² has been made. Measurements of the mechanical properties of the polymers before and after implantation have been made with an ultra microindentation system using both pointed and a small (2 μm) radius spherical-tipped indenter. The surface regions were also investigated by atomic force microscopy (AFM) and Rutherford backscattering (RBS). Significant differences have been observed between the Ti–B dual-implanted surfaces and those of the Au and W implanted surfaces. For both the PET and PS, the resistance to indenter penetration at very low loads was much greater for the Ti–B dual-implanted surfaces. The estimated maximum hardness and modulus of the implanted materials were 0.3 and 8 GPa for the PET material and 1.4 and 16 GPa for the PS material. The results obtained with the spherical indenter show a gradual decline in effective modulus of the surface with penetration depth, whereas the hardness or contact pressure goes through a maximum before declining asymptotically to the bulk values. The values of hardness estimated for the spherical-tipped indenter are somewhat more conservative than the optimistic estimates with the Berkovich indenter. The improved increase in hardness for the Ti–B dual-implanted PET material scales with the RBS measured increased depth of implantation.