Surface “metallization” of poly(tetrafluoroethylene) films with a “synthetic metal”

Surface “metallization” of poly(tetrafluoroethylene) (PTFE) film with a “synthetic metal”, viz., polyaniline (PAN), was carried out chemically and physically to render the PTFE surface electrically conductive. The chemical surface modification involved the UV-induced graft copolymerization of the argon plasma-pretreated PTFE film with 4-vinylaniline (4-VAn) monomer, followed by oxidative graft copolymerization of aniline via the aniline moiety of the grafted 4-VAn polymer. The efficiency of the surface oxidative graft copolymerization with aniline (and thus the resulting surface conductivity) was enhanced by the high concentration of the grafted 4-VAn polymer from the initial graft copolymerization. The surface electrical resistance of the PTFE film so prepared was reduced by more than 10 orders of magnitude to about 10⁶ Ω/□. The physical surface modification involved the coating of PAN on surface-modified PTFE film, prepared from UV-induced double graft copolymerization with acrylic acid (AAc) and sodium salt of styrenesulfonic acid (Na-SSAc), during the oxidative polymerization of aniline. The grafted AAc and SSAc polymers contain the protonic acid groups for the protonation/doping of the coated PAN to result in strong adhesion of the latter and a surface resistance of the PTFE film on the order of 10³~10⁴ Ω/□. The intrinsic redox states and the protonation/deprotonation behavior of the grafted and coated aniline polymer on the PTFE film were grossly similar to that of the aniline homopolymer. The surface compositions of the modified PTFE films were studied by X-ray photoelectron spectroscopy (XPS). Both the grafted and the coated aniline polymer layers exhibited good durability toward solvent extraction.