Chemical interactions between metal ions and polymer surfaces

Date of Completion

January 1990


Chemistry, Polymer




Fluoropolymers may be treated with sodium naphthalenide (Na/naphth) in tetrahydrofuran (THF) or laminated with copper sheet so as to increase their ability to form adhesive bonds with other polymers or metals. First, qualitative and quantitative analysis of the chemical modification which results from Na/naphth treatment were done using a range of derivatizations coupled with infrared (IR), ultraviolet (UV), and X-ray photoelectron (XPS) spectroscopic techniques. The etched layer thickness increased with treatment time, to over 300 nm after 4 hrs Na/naphth treatment. After 60 minutes treatment of a perfluoroalkoxy (PFA) film, the surface was defluorinated to a depth of 115 nm, with almost all the carbons in that region being functionalized in some fashion. Na/naphth treatment introduces C-H, C=O, C-OH, $C{\equiv}C$, and C=C functionalities in the surface of PFA. Carbonyl groups were present at 3.3 $\times$ 10$\sp{-9}$ equivalents/cm$\sp2$ of film surface, which, averaged over the 115 nm affected depth, is equivalent to about 0.25 carbonyls per 100 carbons. The carbonyl content increased with increasing storage time in air. The other major functionalities were alkene (26 per 100 carbons), with a conjugation length of 10, alkyne (18 per 100 C), aliphatic CH (3.5 per 100 C), hydroxyl (0.30 per 100 C), and carboxylic acid ($<$0.02 per 100 C). A comparison of the IR and XPS data shows that the unsaturation was distributed relatively uniformly through the 115 nm, while the carbonyl and hydroxyl species were concentrated in the top few nm. It was also found that the etching rate depended more strongly on the surface area of the fluoropolymer rather than on the fluoropolymer type or surface crystallinity. Of the materials studied, the etching rate increased with increasing surface roughness, but showed no correlation to amorphous and crystalline morphology.^ Also the modification of the fluoropolymer surface by contact with a copper sheet was evaluated using XPS, IR-IRS and DRIFT techniques. An increase of the oxygen content and the carbon-carbon double bond group absorption were identified, but the depth of modification was much less than that of the Na/naphth treatment.^ The interaction of the acid form sulfonated polystyrene (SPS) with metal oxides (iron oxide and copper oxide) was identified using IR-RAS and DRIFT. The interaction was identified as salt formation between $SO\sbsp{3}{-}$ of SPS and the metal oxide. By heating above $T\sb{g}$, the interaction between SPS and a steel shim was increased.^ The above results can be used to optimize the adhesion of fluoropolymers and SPS to other polymers or metals. ^