Excellent Transparency In Visible Region Research Articles

Facile thiol-epoxy click chemistry for transparent and aging-resistant silicone/epoxy composite as LED encapsulant

The thiol-epoxy click chemistry is promising for microelectronic packaging due to its outstanding properties, while there is little knowledge on silicone/epoxy composite fabricated via this approach. Herein, a thiol-functionalized silicone resin (MDT-SH) is synthesized and compounded with epoxy resin to form silicone/epoxy composite. The thermal-curing behaviors, mechanical properties and LED encapsulation of the developed composite are studied detailedly. The thermal-curing kinetics indicate that the thiol-epoxy polymerization in silicone/epoxy composite tends more to the first-order reaction and its active energy is about 60.3 kJ/mol. The mechanical properties of the composite are varied with the molecular structure of MDT-SH and thiol/epoxy ratio. Moreover, the composite has excellent transparency in visible region, and its transparency is little affected by thermal and UV ageing. More importantly, the transparency is only slightly decreased after the composite is serviced at normal temperature and pressure for 2 years. The light output power of LEDs encapsulated by this composite is comparable to the commercial counterparts like Dow Corning OE-6550, but its thermal-curing time and temperature are much lower than the latter, contributing to cost reduction. Therefore, this silicone/epoxy composite based on thiol–epoxy click chemistry would greatly improve the microelectronic packaging.

Preparation and characterization of self-cleaning and anti-reflection ZnO-SiO2 nanometric films

Unlike the general anti-reflection and self-cleaning film such as SiO2 and TiO2-SiO2, the ZnO-SiO2 nanometric film used as a substrate of excellent transparency in visible region and effective photo-catalytic self-cleaning under UV illumination is seldom studied in the application as a substrate; however, it has a lot of advantages including high transmittance and low refractivity. In this paper, a self-cleaning and anti-reflection ZnO-SiO2 nanometric film is successfully fabricated by using a sol-gel dip-coating method. The morphology, crystal structure, surface microstructure and light transmittance of the obtained products are characterized by techniques such as TEM, SAD, XRD, SEM, DTA and UV-vis. Photo-catalytic degradation of the methylene blue (MB) in aqueous solution is used as probe reaction to evaluate the photo-catalytic activity of ZnO-SiO2 nanometric film. The TEM images reveal that the as-prepared ZnO nanoparticles are spherical grains with diameters of 12-20 nm, the average grain diameter is about 14.51 nm. ZnO nanoparticles obtained are of hexagonal wurtzite structure revealed by XRD pattern and there exist no other diffraction peaks, Furthermore, the SAD results show that ZnO microstructurs have good crystallinity. In addition, the ZnO grain size is about 14.41 nm by using the Scherrer formula calculation, which is consistent with the TEM results by the Gauss simulation. The UV-vis spectra reveal that the ultraviolet characteristic absorption peak of ZnO-SiO2 composite films is located at 368 nm and 375 nm after annealing at different temperatures such as 300℃ and 450℃, corresponding to the band gaps of 3.37 eV and 3.31 eV, respectively. It is highly consistent with that obtained from pure ZnO nanoparticles. Increasing the annealing temperature results in a lower refractive index and the increases of the porosity in of the ZnO-SiO2 composite films. It has a uniformly refractive index value about 1.23-1.25 and a high porosity value about 50.3-54.7% when the annealing temperature is 450 ℃. Experimental results show that the ZnO-SiO2 composite film can enhance the light transmittance of the quartz substrate, due to its lower reflective index and higher porosity. Compared with the quartz substrate, the average optical transmission rate of the quartz glass coated with ZnO-SiO2composite films is increased by about 4.17% at 400-800 nm, which favors greatly anti-reflection characteristics in a wide spectrum range. Meanwhile, the ZnO-SiO2 composite films are found to be efficient for photo-catalytically degradation of methylene blue dye under UV illumination, which favors greatly the self-cleaning function.

Femtosecond nonlinear optical property of a TeO2–ZnO–Na2O glass and its application in time-resolved three-dimensional imaging

Compared with bismuth glasses and chalcogenide glasses, tellurite glasses have a wider transparency window. Especially, these glasses with excellent transparency in visible region could offer a larger dynamic range for the time-resolved simultaneous three-dimensional imaging based on the optical Kerr gate (OKG). We investigated the ultrafast nonlinear optical properties of a TeO2–ZnO–Na2O glass using a femtosecond optical Kerr gate at wavelength of 800nm. The nonlinear refraction n2 and the ultrafast nonlinear response time of the tellurite glass were estimated to be 4.56×10–15cm2/W and less than 200fs, respectively. We also demonstrated the time-resolved simultaneous three-dimensional imaging using the tellurite glass as the Kerr medium, which indicated that tellurite glasses may also be good candidates as the Kerr media for the time-resolved imaging based on the OKG.

Controllable properties and microstructure of hydrogels based on crosslinked poly(ethylene glycol) diacrylates with different molecular weights

AbstractThis work describes a comprehensive study of hydrogels based on polyethylene glycol diacrylates (PEGDAs) with the molecular weight (MW) range of 400–2000. The blends of low‐ and high‐molecular weight PEGDA macromers with different ratios were photopolymerized under visible light irradiation, using a blue light sensitive photoinitiator Irgacure819, at the total polymer concentration of 60 wt %. Swelling ratios, wetting property, elastic moduli, transparency, and the microstructure of the resulting hydrogels were investigated. Among them, equilibrium water contents, hydrophilicity, and mesh size of the hydrogels increased while the elastic moduli decreased when increased the PEGDA MW or the content of higher MW PEGDA in the blends. Most of the hydrogels possessed excellent transparency in visible region. The viability of L929 cells on the surface of hydrogel was also estimated. All the selected hydrogels exhibited a relatively high proliferation rate, which demonstrated this hydrogel system with photoinitiator Irgacure819 had good biocompatibility. These results show the properties of PEGDA hydrogel could be easily adjusted by varying PEGDA MW or the ratios of low‐ and high‐MW macromers in the composites. It could be helpful for the design of proper PEGDA hydrogels in the applications as tissue engineering or drug delivery system. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011