Study on the phenylmethylsiloxane-modified epoxy hybrid properties for the use as LED encapsulant

In this study, the properties of diglycidyl ether of bisphenol A (DGEBA)-methylhexahydrophtalic anhydride (MHHPA) modified with phenylmethylsiloxane-modified epoxy (PMSE) after long-term thermal aging condition were studied. The optical and dynamic mechanical properties of the materials, and the effects of these properties on the light output from the encapsulated LEDs, were studied after 150 °C long-term thermal aging condition. The transmittance and dynamic mechanical properties were studied by the spectrophotometer and the dynamic mechanical analysis (DMA). The free volumn of the DGEBA-PMSE hybrids after thermal aging were studied by the positron annihilation lifetime spectroscopy (PALS). The transmittance of DGEBA-PMSE hybrids were much stable than that of DGEBA-MHHPA after thermal aging. However, the luminous flux of DGEBA-PMSE-0.4 encapsulated LEDs was lower than that of DGEBA-MHHPA after 30 days thermal aging because the mechanical properties of DGEBA-PMSE hybrids changed. The storage modulus of DGEBA-PMSE-0.4 increased 26% after 30 days thermal aging and the material became stiffening during the condition. With the decay in the luminous flux of the LED, there was not only decay in transmittance of the material, the dynamic mechanical properties of the material also changed due to the rearrangement of the DGEBA-PMSE molecules. The free volume of DGEBA-PMSE-0.4 was decreased 5.8% that revealed the effect of the thermal aging was the molecular rearrangement and the cured networks could rearrange to more compacted conformation. The relative optical and dynamic mechanical stability of DGEBA-PMSE-0.2 afforded this material the most stable light output of all the encapsulated LEDs.