Surface Modification of Polymer Materials by Excimer 172 nm UV Light

This review article discusses the application of excimer 172 nm ultraviolet (UV) light in altering the physicochemical surface properties of polymer materials, especially poly (ethylene terephthalate) (PET). To evaluate the water contact angle as a measure of wettability, the Wilhelmy method, which enables obtaining a high- precision contact angle at the three-phase boundary, and the conventional sessile drop method were adopted. A remarkable decrease in the water contact angle on the polymer samples ( i. e ., increase in wettability) was accomplished by irradiating the samples with UV light for some tens of seconds. When the UV-treated polymer samples were stored in air, an increase in the contact angle, i. e ., hydrophobic recovery, was observed over a number of days. X-ray photoelectron spectroscopy data showed that the increase in wettability following UV irradiation was attributed to the increased atomic oxygen concentration on the sample surface. Atomic force microscopy revealed surface roughening at the nanoscale following UV irradiation. It was determined by the Wilhelmy method that the UV lithography produced hydrophobic/hydrophilic (unexposed/UV-exposed) mosaic patterns on the polymer surface. Furthermore, UV treatment was applied to improve the performance of the PET fabric as a textile. No significant changes in the surface reflectance and tensile properties of the PET fabric following UV irradiation were observed, suggesting only little UV impact damage. The wettability of a PET single fiber taken from the PET fabric, which was measured by the Wilhelmy method, increased following UV treatment, although the water contact angle on the single fiber varied along the fiber axis, owing to the weave of the fabric. UV oxidation enhanced the water absorbency and detergency of the PET fabric due to hydrophilization of the fiber surface. The roughening of the fiber surface by UV exposure produced a deeply colored PET fabric after dyeing with dispersive dyes.