Hydrophilic group formation on hydrocarbon polypropylene and polystyrene by ion-assisted reaction in an O2 environment

Polystyrene (PS) and polypropylene (PP) films were modified by ion-assisted reaction in order to understand chemical reaction between the polymer and the O-2 gas during low-energy Ar+ ion irradiation and to improve wettability of the polymers to water. The ion dose of Ar+, the ion beam energy, and the oxygen gas flow rate were changed from 5 x 10(14) to 1 x 10(17)/cm(2), from 0 to 1.2 keV and from 0 to 8 ml/min, respectively. Contact angles of water on polymers modified by Ar+ ion irradiation without blowing oxygen gas changed from 76 degrees to around 40 degrees, but those of water on polypropylene and polystyrene modified with blowing oxygen gas drop to 22 degrees and 19 degrees, respectively. X-ray photoelectron spectroscopy analysis shows that the hydrophilic groups were formed on the surface of polymers by chemical reaction between the unstable chains induced by the ion irradiation and the blown oxygen gas, and the hydrophilic groups were identified as -C-O- bond, -(C=O)- bond and -(C=O)-O- bond. The contact angle of water on polymers depends on the hydrophilic groups formed on the polymer surface by the ion-assisted reaction. (C) 1999 Elsevier Science B.V. All rights reserved.