Photochemical Surface Modification of Polytetrafluoroethylene with Hydrazine: Characterization of the Surface with Zeta-Potential Measurements and Spectroscopic Techniques

Surfaces of PTFE were modified by polychromatic UV irradiation in the presence of hydrazine vapors. The surfaces were characterized by FTIR and XP spectroscopy as well as by zeta-potential and contact angle measurements. FTIR spectroscopy revealed that - in addition to the introduction of amino and hydrazinyl groups onto the PTFE surface - a partial hydrogenation of the CF units proceeds (generation of hydrocarbon units CH). This finding is backed by XPS results. A fraction of the photochemically modified PTFE layers is soluble in aqueous media, while hydrogenated units appear to be more stable. The determination of the zeta potential of the PTFE surface showed a shift of the isoelectric point towards higher pH values as a result of the surface modification. The zeta potential vs. pH curves are shifting steadily towards more positive values at increasing duration of the N2H4/UV treatment. The analysis of the surface tension components of hydrazine-modified PTFE indicates a strong increase of the Lifshitz-Van der Waals components and electron-donor components  compared to untreated PTFE. These components change in different fashion after extraction of the PTFE surface with aqueous media. Finally it is shown that amino and hydrazinyl groups at the PTFE surface can be derivatized by polymer-analogous reactions with isothiocyanates and anhydrides.