The notion that individual functional groups on plasma‐modified polymer surfaces or in plasma polymers can be detected and quantified using selectively reacting derivatization reagents has dominated the field of plasma‐based surface technology since more than 30 years. For nitrogenated films and surfaces it has traditionally been believed that amino groups can be analyzed selectively using electrophilic reagents such as benzaldehydes or carboxylic acid anhydrides. This article presents arguments indicating that traditionally applied methodologies are partially based on myths. Presumed amino groups are – at least to a substantial extent – probably in fact other nitrogen‐bearing moieties. It is open to question if primary or secondary amino groups could “survive” the physico‐chemical environment typical of a plasma at all. Advancing the chemical understanding of N‐containing plasma‐generated films and surfaces, and plasma‐chemical formation mechanisms requires rethinking the interpretation of derivatization experiments.

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 N₂/H₂ mixtures and a subsequent exposure of the samples to the ambient air results in the formation of –NH₂ moieties of primary amides on the polymer surface. Corresponding in situ experiments with streaming N₂/H₂ DBD post-discharges virtually free of H₂O and O₂, on the other hand, showing the absence of –NH₂, proving that no primary amines or amides are formed by this treatment although substantial amounts of nitrogen are incorporated. Moreover, directly N₂/H₂-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 C=N 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 C=N bonds and carbon in C=C bonds

A new method for combinatorial area-selective polymer modification or deposition using DBD-type plasmas at atmospheric pressure (“plasma-printing”) is presented. Thereby a gradient of two gases perpendicular to the flow direction is established by triangular-shaped overlapping gas inlets. Design of this reactor allows generation of spot arrays with controlled gradients of physicochemical surface properties which is first applied by investigating the influence of H2 admixtures to N2-plasma-treatment of polymers. Formation of functional groups is quantitatively characterized by ATR FT-IR with preceding chemical derivatization using nucleophilic and electrophilic chemicals. It is shown that treatments using high gas flow velocities are more efficient than treatments with low gas speed. Also it is shown that direct plasma treatment leads to polymer surfaces with nucleophilic and electrophilic properties and that H2 content influences formation of both types of functionalities

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