Critical remarks on chemical derivatization analysis of plasma‐treated polymer surfaces and plasma polymers

Abstract

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.

Low‐pressure plasma treatment for direct amination of L605 CoCr alloy for the further covalent grafting of molecules

“…Nevertheless, there is an ongoing debate for the use of chemical derivatization as a valid quantification method for primary amine groups, therefore the need for supplementary surface characterization. [18] The presence of primary amine groups was also confirmed by ToF-SIMS analyses in static negative mode, with the characteristic fragment NH 2 − (m/z 16.095) displaying a NH 2 − /total peak ratio of 2.2 × 10 −4 after amination, as compared to 2.7 × 10 −6 before, confirming the plasma functionalization. These moieties were used thereafter as anchor points to graft molecules, at which point GA was selected as the linking arm and the grafting of a peptide took place as the next stage of the procedure.…”

“…The selectivity of the MW plasma treatment, namely, the ratio between the primary amines and initial nitrogen amount detected (%NH 2 /%N), was 14.4%. Nevertheless, there is an ongoing debate for the use of chemical derivatization as a valid quantification method for primary amine groups, therefore the need for supplementary surface characterization . The presence of primary amine groups was also confirmed by ToF‐SIMS analyses in static negative mode, with the characteristic fragment NH 2 − (m/z 16.095) displaying a NH 2 − /total peak ratio of 2.2 × 10 −4 after amination, as compared to 2.7 × 10 −6 before, confirming the plasma functionalization.…”

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

“…For ex situ FTIR‐ATR investigations of hydrogen‐deuterium (H/D) exchange experiments, an acrylic plate with a through hole, forming a small chamber around the ATR crystal, was placed on top of the accessory. Prior to measurement, samples were placed in the chamber and the volume was purged with vapors of D 2 O or H 2 O for about 10 s to perform H/D exchange on the treated polymer surface which was immediately followed by ATR measurement …”

Why do we need chemical derivatization?

“…However, the recent paper by Klages and Kotula covers part of this subject in an excellent manner for the very particular field of nitrogen‐based plasma‐functionalized organic surfaces. It provides a comprehensive, critical overview not only about the published literature in the field, but also about its historical progression.…”