CHARACTERIZATION OF THE AGING OF PLASMA-DEPOSITED POLYMER-FILMS - GLOBAL ANALYSIS OF X-RAY PHOTOELECTRON-SPECTROSCOPY DATA

A protocol for global analysis of x-ray photoelectron spectra of plasm a-deposited polymer films is presented. These materials are difficult to analyse because of the multitude of different chemical groups prese nt. The combination of different primary and secondary binding energy shifts results in relatively broad, featureless photoelectron peaks. T he protocol is based on fitting a series of spectra obtained by monito ring the surface composition of a plasma polymer film over extended pe riods of time after deposition. Information obtained from this first r ound of curve-fitting is used in the form of additional constraints fo r a second round of fitting, This leads to a self-consistent procedure which is akin to a global approach to curve-fitting. To illustrate ap plication of this method, results of a study of an n-heptylamine plasm a polymer are described. The spectral changes on ageing provided clear evidence for radical-initiated oxidation reactions. These reactions g enerated additional radicals, which sustained the oxidation process fo r many months and not only led to substantial incorporation of oxygen into the material (forming a variety of carbon-oxygen functionalities) but also to conversion of most of the existing carbon-nitrogen functi onalities to an oxidized form.