The surface structure of UV exposed poly-dimethylsiloxane (PDMS) insulator studied by slow positron beam

In this study, the variations in surface structure of Poly (dimethyl siloxane) (PDMS) composite before and after different UV treatment conditions have investigated using slow positron beam. S profiles of the exposed samples show a broader shallow valley in a low energy range (1–2.25 keV) suggest that a silica-like layer has formed at the surface during UV-treatment, and its thickness could be estimated as 80 nm. Furthermore, corresponding to the range that from ∼180 to ∼360 nm from the surface, the height of the peak in S (E) curve for each UV treated sample has increased with longer exposure time, and the peak position tends toward the low energy side. These features may indicate that, formed by chain scission in situ, a loose structure including more Low weighted molecular (LWM) species has been generated beneath the silica-like layer during the oxidation process. The longer the oxidation process lasts, the more LWM species accumulate beneath the silica-like layer. While, the data obtained from contact angle measurement and X-ray photoelectron spectroscopy (XPS), show less structural change has occurred, which could contribute the LWM species migrate to the topmost surface, resulting covered the useful information.