Inkjet printing of 3D nano-composites formed by photopolymerization of an acrylate monomer

This paper considers inkjet printing of optical quality 3D nano-composites from diethylene-glycol diacrylate monomer (DEGDA) containing ZrO2 nanoparticles at varying concentrations. One application for the composites is for gradient refractive index (GRIN) lenses. The process involves printing of a nanoparticle loaded monomer “ink” onto a substrate and then photopolymerizing the monomer layer by layer using UV light. The results of the study confirm that the presence of nanoparticles favorably affects the reaction kinetics. The reaction rate and chemical conversion are enhanced considerably by the nanoparticles. A seamless interface between the layers, which are 20 μm thick, may be achieved if the conversion level of the layer onto which ink is deposited is limited at 60 to 80%. Dynamic mechanical analysis (DMA) data indicate that both the glass transition and sub Tg viscoelastic properties are influenced by the nanoparticles. When nanoparticles are introduced the Tg relaxation shifts to lower temperatures and a sub Tg relaxation appears whose intensity increases with particle concentration. These results are consistent with a molecular confinement model involving a lower crosslink density rubbery layer at the polymer–particle interfaces.