Surface passivation of epoxy resin with a covalently adhered poly(tetrafluoroethylene) layer

Abstract

Surface passivation of epoxy resin with a covalently adhered poly(tetrafluoroethylene) (PTFE) layer was achieved by casting the epoxy resin on a surface-modified PTFE film, followed by thermal curing and mechanical delamination. Surface modification of the PTFE film was carried out by argon plasma pre-treatment, followed by UV-induced graft copolymerization with acrylic acid (AAc), glycidyl methacrylate (GMA), 2-hydroxyethyl methacrylate (HEMA) and acrylamide (AAm). The compositions and microstructures of the corresponding AAc-g-PTFE, GMA-g-PTFE, HEMA-g-PTFE and AAm-g-PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and water contact angle measurements, respectively. In all cases, the graft yield increased with the argon plasma pre-treatment time of the PTFE film and the monomer concentration. Thermal curing of the epoxy resin on the graft-copolymerized PTFE surfaces (the AAc-g-PTFE and GMA-g-PTFE surfaces, in particular) resulted in strong adhesion of the epoxy resin on the PTFE surface. The strong adhesion arose from the curing of the grafted AAc or GMA chains into the epoxy resin matrix to form a highly cross-linked interphase, as well as the fact that the AAc or the GMA chains were covalently tethered on the PTFE surfaces. The strong adhesion also resulted in cohesive failure inside the PTFE substrate during mechanical delamination to give rise to a passivated epoxy resin surface with a covalently adhered PTFE layer.