Surface characterization of plasma-modified poly(ethylene terephthalate) film surfaces

Poly(ethylene terephthalate) (PET) film surfaces were modified by argon (Ar), oxygen (O-2), hydrogen (H-2), nitrogen (N-2), and ammonia (NH3) plasmas, and the plasma-modified PET surfaces were investigated with scanning probe microscopy, contact-angle measurements, and X-ray photoelectron spectroscopy to characterize the surfaces. The exposure of the PET film surfaces to the plasmas led to the etching process on the surfaces and to changes in the topography of the surfaces. The etching rate and surface roughness were closely related to what kind of plasma was used and how high the radio frequency (RF) power was that was input into the plasmas. The etching rate was in the order of O-2 plasma > H-2 plasma > N-2 plasma > Ar plasma > NH3 plasma, and the surface roughness was in the order of NH3 plasma > N-2 plasma > H-2 plasma > Ar plasma > O-2 plasma. Heavy etching reactions did not always lead to large increases in the surface roughness. The plasmas also led to changes in the surface properties of the PET surfaces from hydrophobic to hydrophilic; and the contact angle of water on the surfaces decreased. Modification reactions occurring on the PET surfaces depended on what plasma had been used for the modification. The O-2, Ar, H-2, and N-2 plasmas modified mainly CH3 or phenyl rings rather than ester groups in the PET polymer chains to form C-O groups. On the other hand, the NH3 plasma modified ester groups to form C-O groups. Aging effects of the plasma-modified PET film surfaces continued as long as 15 days after the modification was finished. The aging effects were related to the movement of C=O groups in ester residues toward the topmost layer and to the movement of C-O groups away from the topmost layer. Such movement of the C=O groups could occur within at least 3 nm from the surface. (C) 2004 Wiley Periodicals, Inc.