The surface modifications of polyvinylidene fluoride (PVDF) induced by rf Ar plasma treatment have been investigated using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Water contact angle measurements on PVDF surfaces were also performed. The XPS analysis shows that the plasma treatment causes dehydrofluorination of PVDF and the incorporation of oxygen into the polymer surface, while the AFM images reveal surface roughening. Contact angle measurements and surface free energy calculations show an improvement in the PVDF surface wettability after the plasma treatment. The decrease of F(1s)/C(1s) ratio and water contact angle and the increase of surface roughness and free energy for rf Ar plasma-treated PVDF prove that both chemical and physical effects play an important role in the adhesion. (C) 1998 Elsevier Science Limited. All rights reserved.