Study of the adhesion and interface of the low-temperature bonding of vacuum ultraviolet-irradiated cyclo-olefin polymer using electron microscopy

Abstract

Surfaces of cyclo-olefin polymers (COPs) are photoactivated by vacuum ultraviolet (VUV) light and can be bonded with a practical bonding strength at low temperatures below T g. The VUV irradiation condition was optimized, the maximum interfacial toughness was obtained for 5 min of irradiation and a longer irradiation time resulted in a decrease in toughness. We also found that a high-humidity environment caused the decrease in toughness. We investigated the mechanism of the low-temperature bonding of COP by characterizing the fracture surfaces using high-resolution scanning electron microscopy and imaging the bonded interfaces using energy-filtering transmission electron microscopy and scanning transmission electron microscopy. The fracture surfaces exhibited a large number of nanofibrils, whose features are similar to those we previously observed in the polymer-polymer interfaces that were welded in melt conditions. We conclude that the interfacial failure occurs where the polymer chains connected at the interface by hydrogen bonding are pulled out. Thus, the entanglement is important in the bonding of polymers by surface-activation processes.