Microencapsulation technology has been increasingly applied toward the development of self-healing paints. Added to paint as a dry powder prior to spraying, the microcapsules store a liquid that can repair the protective barrier layer if released into a scratch. However, self-healing will not occur unless the microcapsules can withstand spray-painting, aggressive solvents in the paint, and long-term exposure to the elements. We have therefore developed a one-pot synthesis for the production of Pickering microcapsules with outstanding strength, solvent resistance, and barrier properties. Octadecyltrimethoxysilane-filled (OTS) microcapsules form via standard interfacial polycondensation, except that silica nanopowder (10-20 nm diameter) replaces the conventional surfactant or hydrocolloid emulsifier. Isophorone diisocyanate (IPDI) in the OTS core reacts with diethylenetriamine, polyethylenimine, and water to form a hard polymer shell along the interface. Compared to pure polyurea, the silica-polyurea composite improves the shelf life of the OTS by 10 times. The addition of SiO2 prevents leaching of OTS into xylenes and hexanes for up to 80 days, and the resulting microcapsules survive nebulization through a spray gun at 620 kPa in a 500 cSt fluid.
Differential scanning calorimetry (DSC) and oscillatory parallel-plate rheometry were used to investigate the curing of an epoxy resin (Dow Quatrex 5010). The viscosity was correlated with the glass transition temperature (Tg) and conversion by aborting the rheometer runs at specified intervals during the cure. The quenched samples were analyzed by DSC to determine the Tg and the conversion. The isothermal Tg-conversion relationship was modeled with the DiBenedetto equation. The Tg and conversion during nonisothermal (dynamic) curing could be modeled by using the DiBenedetto equation and a second--order kinetic equation. The model constants determined from isothermal experiments were used in the nonisothermal calculations.
MULTILAYEREDPRINTED CIRCUIT BOARDS are complex structures consisting of layers of prepreg and copper. The prepreg is fabricated by impregnating woven glass cloth with a catalyzed epoxy resin solution. The solvent is removed, and the epoxy partially advanced in a treater tower, yielding a tack-free, stable prepreg. Typically, several sheets of prepreg are placed between two thin copper foils and laminated under heat and pressure with a hydraulic press. As the prepreg is heated during lamination, the 3
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