Different morphologies of nano-ZnO affection on properties of transparent epoxy resin encapsulants

With the development of light emitting diodes (LEDs), it puts forward higher performance requirements on encapsulants, mainly epoxy resins. So far, people have made a great deal of efforts on improving the thermal conductivity, resistance of thermal and ultra-visible light (UV) aging, visible light (Vis) transparency and refractive index. It is an effective method of introducing inorganic fillers, like zinc oxide (ZnO) and titanium oxide (TiO₂), into epoxy matrix to prepare nanocomposites. In this paper, two morphologies of nano-ZnO, particles and nanorods, were prepared. Nano-ZnO particles and rods were respectively dispersed into butanone with ultrasonic technique before added into the epoxy solution. The epoxy resins were made into ultra-thin film via spin-coating method. The results show that the nano-ZnO particles/epoxy nanocomposite ultra-thin films kept high visible transparency and high UV shielding at the condition of 1wt% addition, but no improvement on thermal conductivity. Contrarily nano-ZnO rods/epoxy nanocomposite ultra-thin films did not present so well in optical properties, but better on thermal conductivity. So we mixed the two kinds of nano-ZnO to improve the thermal conductivity at the presupposition of not harming the shielding of UV and keeping the transparency of Vis of the epoxy resins.