Surface modification of poly(tetrafluoroethylene) films by graft copolymerization for adhesion improvement with sputtered in-sn oxides

Abstract

Surface modification of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) films was carried out via UV-induced graft copolymerization with glycidyl methacrylate (GMA), acrylamide (AAm) and hydroxylethylacrylate (HEA) to improve the adhesion strength with sputtered indium-tin-oxide (ITO). The surface compositions of the graft-copolymerized PTFE films were studied by X-ray photoelectron spectroscopy (XPS). The graft yield increases with increasing monomer concentration and Ar plasma pretreatment time of the PTFE films. The T-peel adhesion strength was affected by the type of monomer used for graft copolymerization, the graft concentration, and the thermal post-treatment after ITO deposition. A double graft-copolymerization process, which involved initially the graft copolymerization with AAm or HEA, followed by graft copolymerization with GMA, was also employed to enhance the adhesion of sputtered ITO to PTFE. T-peel adhesion strengths in excess of 8 N/cm were achieved in the ITO/graft-modified PTFE laminates. The adhesion failure of the ITO/PTFE laminates in T-peel tests was found to occur inside the PTFE films. The electrical resistance of ITO on all graft-modified PTFE surfaces before and after thermal post-treatment remained constant at about 30 Ω/square, suggesting that the graft layer did not have any significant effect on the electrical properties of the deposited ITO.