Adhesion Behavior of Different Annealed Polyphenylquinoxaline Foils Treated Using Low Pressure Plasma

The aim of this study was to investigate the adhesion behavior of polyphenylquinoxaline (PPQ) foils. PPQ foils were initially produced and then annealed in vacuum furnace at different temperatures. The surface of PPQ was activated with GHz-low pressure plasma (lp-plasma) using oxidative (O-2) and noble (Ar, Ar/He) gases. An epoxy adhesive was used to glue the PPQ foil with a sheet of steel. The adhesions of foils were examined using 90 degrees-peel test. Observations from scanning electron microscopy (SEM) and atomic force microscopy (AFM) in addition to the gravimetry measurements were used to interpretate the effects of plasma treatment of adhesion of foils. The results showed that the peeling resistance values were significantly dependent on plasma treatment time and power as well as annealing conditions. In case of PPQ foils where the adhesion was significantly enhanced, it was observed that the fracture changed from adhesion mode at the interface between the adhesive layer and the PPQ foil to cohesive mode, which was seen either in the layer nearby the PPQ surfaces or in the foil itself. Furthermore, furrowed structures were observed at the fracture surface and they were oriented transversely to the peeling direction. SEM and AFM graphs showed that the surface roughness of PPQ foils increased significantly with increasing plasma treatment time and it was more pronounced when using oxidative than noble gas. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39949.