Studying the buried interfacial region with an immobilized fluorescence probe

The properties of a buried epoxy/glass interfacial region were studied by c ovalently grafting a fluorescent probe to the glass surface. A (dimethylami no)nitrostilbene (DMANS) fluorophore was tethered to a triethoxysilane coup ling agent, generating a fluorescently labeled silane coupling agent (FLSCA ). The glass surface was coated with a silane layer that was doped with sma ll amounts of FLSCA. The emission maximum from grafted FLSCA was different than when the dye was dissolved in bulk resin, suggesting a different inter facial structure. When the dye was dissolved in bulk cured resin, a red shi ft in the emission maximum was detected as the resin temperature was increa sed. A distinct break in the fluorescence maximum vs temperature slope was detected at the glass transition of the bulk resin. The slope became larger at temperatures above T-g. A similar break was observed from grafted FLSCA , suggesting that the grafted dye was sensitive to an apparent glass transi tion in the buried interfacial region. The temperature of the apparent inte rfacial transition measured by grafted FLSCA could be lower or higher than the bulk polymer T-g, depending on the initial structure of the grafted sil ane layer.