Chemical modification of poly(ethylene terephthalate) induced by laser treatment

Poly(ethylene terephthalate) (PET) is modified by a 248 nm KrF excimer lase r with high (above ablation threshold) and low (below ablation threshold) e nergy irradiation. The PET surface develops a well-oriented periodic struct ure 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 th e material are characterized by x-ray photoelectron spectroscopy (xps) and contact angles. PET modified by high energy will normally exhibit the depos ition of some yellow to black ionized, carbon-rich debris on the treated su rface, resulting in a reduction of the O/C ratio. In contrast, a PET surfac e modified by low energy leads to oxidation and almost no ablation. The inc reased oxygen concentration on low energy modified surfaces is probably due to a subsequent reaction with atmospheric O-2 during irradiation. Polar ox idized groups like carboxyls are also induced. Contact angle measurements a re in good agreement with these findings.