Identification of hydrophilic group formation on polymer surface during Ar+ ion irradiation in O2 environment

Ar+ ion irradiation on low density polyethylene (LDPE), and polystyrene (PS) was performed in an O2 environment in order to improve wettability of polymers to water and to identify the formation of hydrophilic groups originated from chemical reactions on the surface of polymers. Doses of a broad Ar+ ion beam of 1 keV energy were changed from 5 x 1015 to 1 x 1017/cm2 and the rate of oxygen gas flowing near the sample surface was varied from 0 to 7 ml/min. The contact angle of polymers was not reduced much by Ar+ ion irradiation without oxygen gas. However, it dropped largely to a minimum of 35 degree and 26 degree for Ar+ ion irradiation in the presence of flowing oxygen gas on LDPE and PS, respectively. From x-ray photoelectron spectroscopy analysis, it was observed that hydrophilic groups were formed on the surface of polymers through an ion-assisted chemical reaction between the ion-induced unstable chains and oxygen. The newly formed hydrophilic group was identified as single-bond (C double-bond) single-bond bond and single-bond (C double-bond O) single-bond O single-bond bond. The contact angle of polymer was greatly dependent on the hydrophilic group formed on the surface