Abstract
The aim of this study is to develop a high performance and high light transparent titanium oxide (TiO2)/silicone resin(SR) nanocomposites for light-emitting diode(LED) encapsulant. The nanocomposites were synthesized by utilizing the uniform dispersed silane modified TiO2 nanoparticles in SR matrix . Anatase TiO2 nanoparticles were used as high refractive index filler to fabricate excellent UV resistance, low moisture permeability and high refractive index silicone nanocomposites. There are two parts for fabricating silane modified TiO2/SR nanocomposites in this study. The first part of this study was the fabrication of modified TiO2/SR nanocomposites with low moisture permeability and high refractive index. The surface modification of TiO2 nanoparticles was carried out using both tetraethyl orthosilicate (TEOS) and tetramethoxyl (octadecyl) silane (TMOS) by a two-step sol-gel method. The particle size of TMOS-m-TiO2 observed by TEM was about 20 nm. The results showed that TMOS-m-TiO2 nanoparticles can promote the dispersion of TiO2 in the silicone matrix due to the steric hindrance of octadecyl silane. Specifically, the addition of 0.005 phr TMOS-m-TiO2/SR nanocomposites showed the strong UV absorption, while still maintain high transmittance within the visible light region(T=82% at 450 nm). The refractive index of the prepared hybrid adhesives can be tuned by 0.010 phr TMOS-m-TiO2 from 1.518 to 1.536. Both of the thermal and UV exposure resistance properties of TMOS-m-TiO2/SR nanocomposites were higher compared to those of commercial available silicone resin due to the strong UV absorption of TMOS-m-TiO2. It was also found that the water vapor transmission rate (WVTR) property of the 0.005 phr TMOS-m-TiO2/SR nanocomposites decreased from 20.1 g/m2•day to 13.5 g/m2•day. The second part of this study was the preparation of modified TiO2/SR nanocomposites via in-situ hydrosilylation reaction during the curing process. By a two-step sol-gel method, TiO2 nanoparticles were grafted by using both tetraethyl orthosilicate (TEOS) and 3-methacryloxypropyltrimethoxy silane (MPTS). TEM studies exhibited that the average diameter of MPTS-m-TiO2 nanoparticles was about 20 nm. The structure of the nanoparticles was analyzed by FTIR, XPS and XRD. The MPTS-m-TiO2 nanoparticles containg vinyl silane groups showed better dispersion in the silicone resin matrix due to the formation of cross-linking structure with silicone resin matrix. The nanocomposites containing 0.005 phr MPTS-m-TiO2 not only possesses high transparency within visible light region(T=85.6% at 450 nm), high UV-shielding efficiency, high refractive index (n=1.56 at 598 nm) but also shows high thermal and UV stability. Morever, the tensile strength of the addition of 0.005 phr MPTS-m-TiO2/SR nanocomposites increased from 0.80MPa to 0.956 MPa. The WVTR of the addition of 0.010 phr MPTS-m-TiO2 /SR nanocomposites were decrease from 14.9 g/m2•day to 6.5 g/m2•day of neat silicone resin. These results suggest that such silane modified TiO2/silicone resin nanocomposites have potential applications for LED encapsulant.