Thermal analyses of dye Disperse Red 1 grafted onto silica nanoparticles

Abstract

Dye-grafted silica nanoparticles (GSiO2) were synthesized via a dual-step process involving, first, attachment of the organic dye Disperse Red 1 (DR1) to the coupling agent, 3-isocyanatopropyltriethoxysilane, by means of urethane bonds, and then grafting of the silylated-DR1 onto silica nanoparticles (~6 nm) prepared by hydrolysis and condensation of tetraethoxysilane in a sol–gel process. Dye-adsorbed silica nanoparticles (DSiO2) were also prepared for comparison, for which DR1 was bound only physically to silica instead of covalent bonds. The thermal behaviors of the formed GSiO2 and DSiO2 were examined by means of differential scanning calorimetry and thermal gravimetric analysis. The results showed that both the particle size and silica content have significant effects on the thermal behaviors of the dye-adsorbed and dye-grafted silica. Moreover, crystalline DR1 lost significantly its crystallinity after being adsorbed on silica, and became virtually amorphous after being grafted onto silica. The formed particles were UV-cured with a multifunctional acrylic monomer to yield color coatings on glass substrates. UV–visible spectra indicated that brightness and color saturation of the coating comprising GSiO2 could be maintained better than that comprising DSiO2 after heat treatment at 280°C.