Effects of low-energy electron bombardment on the surface chemical structure and adhesive properties of polytetrafluoroe
- PDF / 698,534 Bytes
- 7 Pages / 594 x 810 pts Page_size
- 33 Downloads / 209 Views
I. INTRODUCTION The effects of various types of electron and photon radiation on the structure of polymer surfaces is a subject of considerable interest because the types of radiation encountered in various environments (including surface analytical studies) can cause damage to organic materials. In addition, radiation can be used to modify the polymer surface to improve adhesion and other properties. Polytetrafluoroethylene (PTFE) has been studied extensively in this regard because of its many technological applications and because the C( Is) levels for — CH 2 and — CF2-type species are sufficiently well resolved that changes in the surface chemical structure can be observed readily by x-ray photoelectron spectroscopy (XPS). 1 Clark and co-workers2 have used XPS to explore the chemical changes of an ethylene-tetrafluoroethylene copolymer caused by exposure to an Ar plasma. Plasma exposure was observed to defluorinate the surface region and induce cross-linking of the carbon chains. Subsequent XPS studies on PTFE have shown that bombardment by Mg(Ka) x-rays3 and 2000 eV electrons4 lead to similar changes in surface structure. These effects have been shown to improve the adhesion of PTFE to thin metal films evaporated in situ.5 Chemical etching of PTFE with an alkali metal suspended in an organic solvent is commonly used to improve adhesion with other polymers and a major effect of this treatment is also defluorination.6 J. Mater. Res. 1 (5), Sep/Oct 1986 http://journals.cambridge.org
The effect of bombardment of PTFE by low-energy electrons ( S 1500 eV) is interesting because the depth of modification can be confined to the surface region, i.e., the first 10-100 A. This is due to the short mean free path for electrons of these energies in polymers,1'7 and any modification induced by such bombardment should have a modification depth on the order of the mean-freepath length. In contrast, plasma methods (with exposure to ultraviolet radiation) can result in chemical bond scission to depths of several micrometers,2'8 and chemical etching can result in modification depths on the order of millimeters.6 In addition, it is well known that for many types of semiconductors, electron bombardment in the presence of a reactive gas leads to adsorption of functional groups at the surface.9 Such electron-induced adsorption has not been studied extensively for polymer surfaces, but exposure of polymers to plasmas containing reactive gases such as NH 3 causes the adsorption of nitrogencontaining functional groups at the surface, which may improve adhesion.810-11 If low-energy electron bombardment of PTFE can induce chemical changes in a shallow depth of the near surface region ( < 100 A), which result in improved adhesion to other polymers (e.g., epoxies), then this process may be competitive with more conventional methods of improving adhesion. In this paper we report the chemical changes induced in PTFE by low-energy electron bombardment
0003-6951 /86/050717-07S01.75
Downloaded: 16 Mar 2015
© 1986 Materials Research Society IP
Data Loading...
