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Selected Functionalization of Polymer Surfaces by Plasma Immobilization of Functional Molecules M. K. Shi, X. Y. Gong,(a) G. L. Graff, J. D. Affinito,(a) and G. J. Exarhos Supported by PNNL Laboratory Directed Research and Development. (a) Environmental and Health Sciences Division. The ability to modify polymer surfaces while retaining their bulk properties is very attractive for applications in wetting, adhesion, biocompatibility, sensing, wastewater treatment, heavy metals removal, and radioactive isotope removal. Controlled functionalization of the surface with specific chemical groups is a key issue for understanding surface interactions and for maximized surface performance. The objective of this project is to explore a new, vacuum-based technology to selectively graft functional groups onto polymer surfaces. It applies the chemical reactions between the free radicals created on the polymer surface by plasma treatment and the vinyl bond of the functional molecules to chemically graft the functional groups. Our initial effort was focused on developing an in-situ experimental tool (Figure 6.11) so that the grafting experiments and all the surface characterization could be conducted in vacuum to avoid surface contamination, free-radical quenching, or post-treatment reactions due to atmospheric exposure. The system consists of a remote microwave (2.45 GHz) plasma source and a vacuum chamber linked to an XPS analytical instrument. The chamber is equipped with a liquid monomer tank for in-situ grafting reactions, a precision manipulator for in-situ sample transfer, and a DC magnetron sputtering cathode for thin film deposition. Figure 6.11. EMSL’s new in-situ surface modification/film deposition capability. Since the nature and the concentration of free radicals determine the grafting reactions, the first series of experiments were focused on identifying the free radicals created on the surface. Electron spin resonance revealed that the free radicals created on the polyethylene-terephthalate (PET) surfaces were dominated by peroxy (R-O-O·) and polyenyl (R-C=C-C·) species, whose density reached 5 x 1012 spins/cm2 under optimized treatment conditions. Grafting experiments were performed in situ by exposing the plasma-treated surface to a vapor of allylamine molecules. Figure 6.12 shows the comparison of the XPS spectra of untreated and O2 plasma-treated PET surfaces after exposure to allylamine molecules. The N1s peak representing the grafted allylamine molecules can be clearly observed on the O2 plasma-treated PET surface, but it is totally absent on the untreated surface. The amount of grafted amine groups was found to increase with both the vapor pressure of the allylamine molecules and the exposure time. A monolayer of allyamine molecules was grafted onto the surface within 2 hours at a vapor pressure of 500 mTorr. Separate experiments indicate that the grafted amine groups are chemically bonded to the substrate. These results clearly demonstrate the potential of this in-situ capability for selected grafting of functional molecules onto polymer surfaces. Figure 6.12. In-situ XPS demonstration of plasma-grafted amine functional groups. William R. Wiley Environmental Molecular Sciences Laboratory Feedback: webmaster@emsl.pnl.gov Revised: June 12, 2001 Security & Privacy PNNL-13147