In Situ Mass Spectrometry of Polymerising Pulsed Plasmas

Abstract

Pulsed plasma polymerisation provides an efficient method for the functionalisation of solid surfaces. In comparison to continuous wave plasma conditions, it causes limited monomer fragmentation and leads to high levels of structural retention. Diagnostic studies on such systems have become increasingly common establishing plasma diagnostic techniques as a powerful tool to garner a deeper understanding of the chemistry on which these pulsed plasma deposition processes rely on. In this work, in situ time-resolved mass spectrometry was employed, operating in both ion and radical species detection mode, to explore the complex nature of the chemical reactions occurring in the plasma phase. The intent of this project is gain insight into reaction pathways of pulsed plasmas, and draw comparisons between conventional step-growth polymerisation (monomer-monomer addition) and pulsed plasma polymerisation routes. Common monomer precursors were investigated under pulsed plasma conditions, namely; 1-decene, allyl glycidyl ether (AGE), hexafluoropropylene oxide (HFPO), glycidyl methacrylate (GMA), maleic anhydride (MAH) and butyl acrylate (BA). The experimental results confirm that step-growth polymerisation occurs in the plasma phase, via two distinct plasma environments as identified by time-resolved mass spectrometry. Importantly, pulsing electric discharges is demonstrated to limit the monomer fragmentation so that the chemical features of the original monomer precursor remain intact leading to structurally well-defined plasma polymers. Such findings corroborate the results obtained from the characterisation of resulting plasma polymer films that can be found in the literature.