Polytetrafluoroethylene (PTFE) is used in quake-absorbing structures because of its low friction characteristic. Because of its low surface energy, however, a pristine PTFE surface exhibits difficulty adhering to other substances. Consequently, PTFE surface normally requires some pretreatment such as chemical modification before adhesion. We herein propose a new surface modification route for adhesion enhancement of PTFE/epoxy resin interfaces using plasma-assisted morphological and molecular designs. Plasma processing methods under air and in water were used to introduce the peroxide radical and porous structures onto the PTFE surface. Subsequently, a polyethyleneimine derivative having primary amino groups at the molecular end in the side-chain was chemically modified by graft copolymerization to introduce reactive functional groups on the surfaces against epoxy resin-based glue. We achieved enhancement of T-peel strength between the PTFE substrate/ epoxy resin/ SUS substrate of 9.3 N/mm, which exceeds the T-peel strength obtained from conventionally used sodium-naphthalene processing (9.1 N/mm).
For application to synthetic resin parts and to the fabrication of microfluidic devices made of cyclo-olefin polymer (COP), an adhesiveless bonding technology was developed: photo-activation bonding. A Xe excimer lamp irradiating vacuum ultraviolet (VUV) light of 172 nm wavelength was used as a light source for COP surface modification. The surface modification procedure is extremely simple. A COP plate placed in air with atmospheric pressure is irradiated with the VUV light. Based on VUV photochemistry assisted with atmospheric oxygen, a modified layer including large amounts of polar functional groups (-OH, -CHO, -COOH, etc.) is formed on the COP plate. The VUV-modified COP plates were bonded at a low temperature through attractive interactions between the modified layers on the COP plates without deforming the plates＇ preformed microstructures. A strength test of bonding was conducted to elucidate the effects of surface modification and bonding conditions such as VUV-irradiation distance (dVUV), VUV-irradiation time (tVUV), bonding pressure (PB), bonding temperature (TB), and bonding time (tB).