Modification of surface mechanical properties of polycarbonate by ion implantation

Industrial use of polymers ranges across a broad field of structural, mechanical, electrical and optical applications. In many situations, e.g. in biomedical or optical uses, wear resistance is one of the main requirements. Ion bombardment of polymers is thought to have great potential for improving some surface mechanical and tribological properties. In particular, high-energy bombardment of light ions is reported to produce relevant increases in hardness and wear resistance. The reason seems to be cross-linking effects induced by the dominant mechanism of the stopping power: electronic loss of energy (for heavier and slower ions, nuclear loss of energy produces breakage of polymer chains and a decrease in hardness). This paper presents a study on the effects induced by implantation of light ions on polycarbonate used in optical applications. Different doses below 1016 ions/cm2 of hydrogen, deuterium, nitrogen and silicon were implanted and microindentation tests were carried out. Although results showed harder surfaces in all cases, except for silicon implantation, the biggest increases in hardness (by a factor three) corresponded to hydrogen and deuterium implantation at high doses. The paper studies the correlation between these results and the estimated electronic energy loss. The optical transmittance was also measured.