Improved Surface Energy Analysis for Plasma Treated PET Films

Wetting experiments in PET/polar liquid systems performed at 25 degrees C in air have shown that the values of contact angle measured one day after PET treatment with He and He/O-2 plasmas decrease significantly compared to the untreated PET. Higher oxygen content in the He plasma improves wetting, whereas the substrate bias and total gas pressure (500 and 750 mTorr) are of minor importance. The calculated absolute values of the surface energy of plasma treated PET films combined to XPS measurements proved that the surface modification enhances their polar component while the dispersive one remains practically unaffected. Moreover, the results have shown that only a part of the polar interactions contribute to the wettability performance assuming that all the dispersive components interact at the solid/liquid interface.