Modification of poly(tetrafluoroethylene) and gold surfaces by thermal graft copolymerization for adhesion improvement

The adhesion between a poly(tetrafluoroethylene) (PTFE) film and a gold sub strate was achieved by surface graft copolymerization of glycidyl methacryl ate (GMA) on an argon plasma-pretreated PTFE film at elevated temperature w ith simultaneous lamination to a surface-modified gold substrate. The plasm a pretreatment introduces peroxides which are thermally degraded into radic als to initiate the graft copolymerization of GMA on the PTFE surface. The gold surface, on the other hand, was first pretreated with 3-mercaptopropio nic acid (MPA), 3-mercaptopropionic acid-2-ethylhexyl ester (MPAEE), or (3- mercaptopropyl)trimethoxysilane (MPTMS) to form self-assembled monolayers ( SAMs) and then subjected to Ar plasma treatment. The simultaneous graft cop olymerization and lamination of the PTFE film to the gold surface was carri ed out in the presence of GMA and an amine hardener at an elevated temperat ure under atmospheric conditions. The modified surfaces and interfaces were characterized by X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The gold/GMA/PTFE assembly exhibited a T-peel adhesion streng th above 10 N/cm and the joint delaminated by cohesive failure inside the b ulk of the PTFE film. The strong adhesion of the Au/PTFE laminate is the re sult of concurrent graft copolymerization on both the Ar plasma-pretreated PTFE surface and the SAM of the Au surface to form a covalent network. The network is further strengthened by the crosslinking reaction promoted by th e presence of the hardener.