THE ORIGIN OF CRITICAL RELATIVE HUMIDITY IN ADHESION

摘要

The fracture behaviors of poly(n-alkyl methacrylate)s (PAMA)/glass joints were investigated using shaft-loaded blister tests over a range of relative humidity (RH). The presence of a critical RH where sudden adhesion loss took place was clearly evident for PMMA and PEMA/glass joints; while such a critical range was absent for the PPMA and PBMA/glass joints. Particular emphasis has been placed on elucidating mechanisms of moisture attack under dry (ca. 2 % RH) and wet (ca. 100 % RH) conditions. The adhesive fracture energy, G_C, was relatively high in the dry environment for the glassy PMMA and PEMA, and the predominant failure mode was cohesive, as indicated by attenuated total-reflection Fourier transform infrared spectroscopy. For the PPMA and PBMA/glass joints, the analogous cohesive failure was found to occur at relatively low G_C values. In the wet environment, the G_C decreased significantly for PMMA and PEMA and the predominant failure mode changed from cohesive to interfacial failure. Conversely, there was no or little depreciation in the values of G_C for the PPMA and PBMA/glass joints in the wet environment. The fundamental mechanism governing the relationship of G_C and RH for the different PAMAs appears to be related predominately to their rheological properties.