Towards the understanding of plasma polymer film behaviour in ethanol: A multi-technique investigation

Plasma polymer films (PPFs) of allylamine are prepared varying the mean power injected in the plasma (P_mean). The PPF behaviour in ethanol is studied through the analysis of the PPF physico-chemistry and the composition of the resulting ethanol solutions. By Visible light Spectroscopic Ellipsometry (VISSE), it is observed that the well-known decrease of the PPF thickness (Δd) upon immersion decreases as a function of P_mean. This behaviour is attributed to an increase of the PPF cross-linking density (χ). By means of time-of-flight secondary ion mass spectrometry (ToF-SIMS) and further statistical processing of the data by principal component analysis (PCA), we propose a method to discriminate the samples according to χ. A significant increase in the PPF oxygen content is also observed after immersion which is ascribed to reaction between ethanol molecules and trapped radicals of the PPF network. On the other hand, taking into account the specificities of the gas chromatography-mass spectrometry (GC-MS) method, the resulting ethanol solutions are demonstrated to be free of chemical species containing a number of carbon atoms ranging from 7 to 40. However, Δd (accounting for PPF restructuring) might come with the dissolution of PPF materials having less than 7 carbon atoms.