Investigation of the surface structures and dynamics of polyethylene terephthalate (PET) modified by fluorocarbon plasmas

Polyethylene terephthalate (PET) surfaces were treated with CH4/CF4 plasmas and the surface structures as well as the dynamic behaviour of the modifie d surfaces after water immersion were studied using angle-dependent x-ray p hotoelectron spectroscopy (XPS), It was found that the fluorocarbon plasma treatment resulted in the formation of some fluorine-containing groups, whi ch improve the surface hydrophobicity of the PET films, The extent of surfa ce modification is dependent on the molar ratio of the CH4/CF4 feed gases u sed in the plasma. The hydrophobicity of the modified PET films decreased a fter they were immersed in water, partly as a result of the 'turnover' or m ovement of the fluorine-containing groups from the surface to the bulk. Fro m XPS analysis, it was found that the movement of the fluorine-containing g roups depends on the modified surface structures. The turnover rates can be described by a decay constant Ic of surface dynamics; the larger the k val ue, the faster the movement of the fluorine-containing groups. Experiments showed that the degree of surface modification is higher and is maintained for a longer period for CH4/CF4 mixed plasmas as compared to that treated b y pure CF4 plasma, The effect of the molar ratio of CH4/CF4 feed gases and its relationship with the movement of the fluorine-containing surface group s were discussed, Copyright (C) 1999 John Wiley & Sons, Ltd.