Chemical Modification of Poly(ethylene Terephthalate) Induced by Laser Treatment

Poly(ethylene terephthalate) (PET) is modified by a 248 nm KrF excimer laser with high (above ablation threshold) and low (below ablation threshold) energy irradiation. The PET surface develops a well-oriented periodic structure of hills and grooves or a “ripple structure” with high energy treatment. However, the ripple size can be reduced to submicron level by irradiation of the sample below the ablation threshold. Chemical surface changes of the material are characterized by x-ray photoelectron spectroscopy (XPS) and contact angles, PET modified by high energy will normally exhibit the deposition of some yellow to black ionized, carbon-rich debris on the treated surface, resulting in a reduction of the O/C ratio. In contrast, a PET surface modified by low energy leads to oxidation and almost no ablation. The increased oxygen concentration on low energy modified surfaces is probably due to a subsequent reaction with atmospheric O 2 during irradiation. Polar oxidized groups like carboxyls are also induced. Contact angle measurements are in good agreement with these findings.