The use of adhesive bonding in joining of materials with different characteristics is of major importance in a variety of microelectronic and photonic applications. The curing of such adhesives is also of great consequence, with the use of optical radiation for adhesive curing becoming the method of choice in various applications, especially bonding of components in microelectronics and fiber-optic assembly. This article reviews recent advances in the development of adhesives, their applications, and their curing methods using optical radiation; it also includes a brief overview of the adhesion mechanisms.
A novel route for morphological characterization of phase separating toughener and cross-linker for epoxy matrices has been investigated using fluorescence spectroscopy. Phase behavior of the individual components is determined by attaching different fluorescent probes to the toughener and cross-linker. In contrast to other techniques such as transmission eletron microscopy (TEM), this method allows resolution between similar components in which selective staining cannot be achieved.
Environmental regulations are forcing the reformulation of many decorative and protective coatings systems. In particular, air-drying solventborne alkyd paints need to meet increasingly stringent emission limits and often must be reformulated with suitable exempt solvents or reactive diluents to achieve volatile organic compound (VOC) reduction. In the research summarized in this article, a new reactive diluent, tetra(2,7-octadienyl) titanate, was synthesized and evaluated in alkyd formulations for VOC reduction and property enhancement. A soy-based long-oil alkyd resin; a soy-based high-solids, long-oil alkyd resin; and a linseed-based, high-solids long-oil alkyd resin were evaluated in combination with the new reactive diluent at weight percentages ranging from 10% to 50%. Characterization included measuring viscosity, film dry times, and film performance of the reactive diluent formulations in comparison to neat alkyd resins used as control. The tetra(2,7-octadienyl) titanate formulations consistently exhibited reduced viscosities and dry times as a function of concentration. The resulting films were harder and more thoroughly cured than the control systems.
Reproducible and uncharacteristic tensile stressstrain behavior of cured glassy epoxy-amine networks produces distinctive fracture surfaces. Test specimens exhibiting plastic flow result in mirror-like fracture surfaces, whereas samples that fail during yield or strain softening regions possess nominal mirror-mist-hackle topography. Atomic force microscopy and scanning electron microscopy reveal branched nodule morphologies in the 50-nm size scale that may be responsible for the unusual tensile properties. Current hypothesis is that plastic flow of the glassy thermoset occurs through the existence and deformation of these nodular nanostructures. The thermal cure profile of the epoxy-amine thermoset affects the size and formation of the nodular nanostructure. Eliminating vitrification during thermoset polymerization forms a more continuous phase, reduction in size of the nodules, and eliminates the capacity of the material to yield in plastic flow. This maximizes nanostructure connectivity of the glassy epoxyamine thermoset and reduces strain to failure significantly.
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