| Compared to ordinary polymer material, the characters of silicone are high heat resistance, low temperature resistance, good weathering resistance and insulation, strong hydrophobicity, high transmittance, good lubrication, sealing and adhesion. In the production of white LED package, Fluorescent slurry is made by mixing phosphor powder and PDMS, then coated on the surface of the semiconductor chip. The invisible ultraviolet light is absorbed by the slurry and then converted to the longer wavelength visible light. It is a simple operation method to get uniform, brightness and stable light source. With the power of HB-LED increasing, large amounts of ultraviolet radiation and heat generated during LED Chip operation. Therefore, the performance of PDMS composites should be improved to meet applied requirements, such as by widely adding filler. In order to improve the organic silicon compounds to be used in the LED products, in this experiment, inorganic particles were added in the polydimethylsiloxane, and the influence of photodegradation of the different particles in the composites, the changes of thermal properties and the reaction mechanism of SiO2/PDMS composites were studied.In this paper, TiO2, ZnO+ZnAl2O4and SiO2particles were prepared by microemulsion method and their surface modified by KH570, MS and SiOx. These particles were prepared by solution blending in the inorganic particles/silicone composites, and the impact of material properties after adding the different particles were studied by UV aging. Under the same environmental conditions, the impact of photodegradation treated by UV aging was analyzed by measuring the temperature changes of the composites with adding Si3N4, BN and SiO2. Moreover, SiO2/silicone composites was analyzed to explore the mechanism of the influences of adding inorganic particles on the composite. Infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetry (TG), UV-Visible (UV-vis), abbe refractometer, infrared thermal imager and shore hardness tester were used to characterize the comprehensive of photodegradation reaction to analysis of the mechanism of the action of organic silicon compounds. The experimental results showed that:(1) Inorganic particles were prepared by the microemulsion method, and the morphologyof the particles were uniform and the size could be control. Morever, the interface compatibility of the particles was improved by silane coupling agent KH570, SiO2and MS modified.(2) The resistance to photodegradation was improved by adding inorganic particles in the composites. The inorganic particles could enhance the ultraviolet radiation absorption and reduce the photocatalysis. Particles were modified by different processes and transformation of crystal to change photodegradation performance of the composites.(3) The trace addition of inorganic particles formed the island model and reduced the thermal conductivity in the composites. When the particles were sufficiently small and the dispersion was uniform, the heat conduction channel could formed, which significantly enhance the rate of the thermal conductivity of the composites.(4) After UV aging, the main chains of silicones were cleavage, which lead to produce a large number of free radicals. Meanwhile, the thermal energy storage increased and the thermal conductivity decreased. Compare to the original one, the sample adding a large proportion of particles could form more thermal conductivity channels to dissipate heat after UV aging,. (5) A large number of free radicals were generated in polymer photodegradation reactions. The hydroxide radicals on the surface of the SiO2particles could react with the residual TEOS, which can prevent the occurrence of the secondary cross-linking reaction. Combined with Mie theory analysis of composites, the extinction cross section radius of SiO2particles gradually increased after photodegradation reaction. When the particle cloud was formed between the particles, the transmittance of the material was a sharp decline. |
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