Use of Free Radicals on the Surface of Plasma Polymer for the Initiation of a Polymerization Reaction

A novel approach to functionalize plasma polymer films (PPFs) through the grafting polymerization initiated from free radicals trapped in the film was developed in this work. 2-Ethylhexyl acrylate (EHA) was chosen as radically polymerizable monomer given the wide use of its corresponding polymer in coating and adhesive applications. The occurrence of the grafting was first confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS). Then grafted chains were studied in more detail. The thickness of grafted chains was quantitatively estimated by angle-resolved XPS (ARXPS), while their morphology and interfacial behavior were qualitatively investigated by atomic force microscopy (AFM), contact angle measurements, and quartz crystal microbalance (QCM). The latter technique provided additional insights regarding the swelling behavior of the grafted layer and its stability upon exposure to challenging environments. Reported scientific findings suggest to use this approach for the covalent binding of a very thin layer on the top surface of a PPF without affecting its bulk properties.