IR‐ and NEXAFS‐spectroscopic characterization of plasma‐nitrogenated polyolefin surfaces

Modification of polyethylene and polypropylene surfaces by atmospheric‐pressure plasmas using mixtures of nitrogen and hydrogen was studied using Fourier‐transform infrared spectroscopy in the attenuated total reflection mode (FTIR‐ATR) and by near‐edge x‐ray absorption fine structure spectroscopy (NEXAFS) in order to shed some light on the chemical nature of nitrogen‐containing functional groups on the polymer surface. Using FTIR‐ATR spectroscopy combined with hydrogen‐deuterium isotope exchange of active hydrogen atoms, it was shown that the direct treatment of PE foils by dielectric barrier discharges (DBDs) in N 2 /H 2 mixtures and a subsequent exposure of the samples to the ambient air results in the formation of –NH 2 moieties of primary amides on the polymer surface. Corresponding in situ experiments with streaming N 2 /H 2 DBD post‐discharges virtually free of H 2 O and O 2 , on the other hand, showing the absence of –NH 2 , proving that no primary amines or amides are formed by this treatment although substantial amounts of nitrogen are incorporated. Moreover, directly N 2 /H 2 ‐plasma‐treated polymer surfaces, similar to afterglow‐treated low‐density polyethylene (LDPE), show amphiphilic character as to be seen by chemical derivatization with nucleophilic reagents 4‐(trifluoromethyl)phenylhydrazine and 4‐(trifluoromethyl)benzyl­amine, in addition to electrophilic aromatic aldehydes normally used to derivatize such surfaces. The presence of imines or other functional groups with CN moieties which may be invoked to explain the dual (amphiphilic) reactivity is proven by NEXAFS studies on ultrathin plasma‐treated PE films, confirming significant amounts of nitrogen in CN bonds and carbon in CC bonds.