Preparation And Optical Properties Of Functional Transparent Silicone Nanocomposites

Due to the unique optical properties of transparent luminescent composites, they have shown a great potential to be applied in optoelectronic devices, light-emitting diodes and paints. Combination of transparent polymers and quantum dots (QDs) leads to development of functional transparent polymer composites that have unique photoluminescent properties. In this dissertation, ZnO-QDs, ZnO-QDs/SiO2 and CdSe-QDs were prepared and used to fabricate silicone nanocomposites with interesting fluorescent properties. Moreover, ZnO/SiO2 nanoparticles were also employed to examine the effect of their size and composition on the transparency or transmittance of silicone nanocomposites. The major results are presented as follows:(1) ZnO-QDs with three different sizes were synthesized via a sol-gel method and then the transparent ZnO-QDs/silicone nanocomposites were subsequently prepared via the solution direct-mixing method. ZnO-QDs with different sizes show different positions of fluorescence peaks and the red shifts are observed as the quantum dots grow up. The addition of ZnO-QDs has little effect on the structure and heat resistance of silicone matrix. As the content of ZnO-QDs increases, ZnO-QDs would agglomerate, leading to the reduced transmittance of silicone nanocomposites. ZnO-QDs/silicone nanocomposites with different sizes of ZnO-QDs can emit different colors just like ZnO-QDs alone do, indicating that the nanocomposites can be prepared with adjustable luminescence by controlling the size of ZnO-QDs.(2) ZnO-QD/SiO2 (Z-S) nanoparticles were synthesized by hydrolyzing TEOS within the ZnO-QD containing ethanol solution. Silica, which enwrapped ZnO-QDs, can effectively prevent the aggregation and growth of quantum dots. Three different sizes of as-prepared ZnO-QDs were used and the Z-S composite particles containing different sized ZnO-QDs show different emission peaks. Moreover, the Z-S composite particles possess phosphorescent properties, and the size of ZnO-QDs shows an effect on the phosphorescence position but no influence on phosphorescence lifetime. Then transparent Z-S/slilicone nanocomposites were successfully prepared in terms of the matrix-filler RI matching principle and the best transparency was achieved when ZnO-QDs content in Z-S composite nanoparticles was 47 wt%. Z-S/silicone nanocomposites have the similar fluorescence and phosphorescence properties as Z-S composite particles do, and the intensities of fluorescence and phosphorescence increase with the increase of filler content.(3) In order to further investigate the transparency or transmittance of composites prepared by the matrix-filler RI matching principle, ZnO/SiO2 (Z-S) composite particles with larger sizes of ZnO were employed to examine the effect of their size and composition on the transparency or transmittance of silicone nanocomposites. The effective refractive index of Z-S composite particles can be changed at various ratios to match the refractive index of silicone and made a better transmittance of Z-S/silicone nanocomposites. When the ZnO content in Z-S composite nanoparticles was 47 wt% at which the refractive index of Z-S composite nanoparticles matched with that of silicone matrix best, the transmittance of the composites reached the optimal value but the size of ZnO showed an influence on the composite transmittance. The transparency decreased as the size of ZnO increased.(4) While it is difficult to get red fluorescence from ZnO-QDs, CdSe-QDs, with the bulk bandgap of 1.72 eV, can be prepared with full color emission. CdSe-QDs were prepared by a solvothermal method. Cd(Ac)2·2H2O and Na2SeSO3 were used as precursors to synthesize CdSe quantum dots with different sizes at different temperatures. Meanwhile, smaller CdSe quantum dots with emission in blue region were gained by an oxidation etching approach using H2O2 as oxidant. The CdSe/silicone nanocomposites were prepared via solution mixture method. The optical properties of CdSe/silicone nanocomposites with different sizes of CdSe-QDs and different contents of CdSe-QDs were studied. With different sizes of CdSe-QDs, the nanocomposites show different colors, which means that the UV-vis absorption position of nanocomposites was affected by the size of CdSe-QDs. Moreover, CdSe/silicone nanocomposites with different size of CdSe-QDs can emit lights with different colors, indicating that the transparent CdSe/silicone nanocomposites with adjustable luminescence can be prepared by controlling the size of CdSe-QDs. As the CdSe-QD content increased, CdSe/silicone nanocomposites showed a decreased transparency while an increased fluorescence intensity.