| Summary: | 博士 === 國立交通大學 === 材料科學與工程系所 === 95 === Preparation and characterizations of the photo-curable organic/inorganic nano-hybrids for OLED packaging are carried out in this study. The experimental works can be classified into two portions: the first is relating to the polymer/clays nanocomposite resins. After clays-modification with synthesized surfactants, the modified clays, or called the acrylateclays were respectively added into photo-curable co-polyacrylate and epoxide resin matrices. The applicability to OLED packaging of epoxide/acrylateclays nanocomposite resin was evaluated by characterizing the lifetime of devices. The second part studies the preparation and characterizations of photo-curable co-polyacrylate/SiO2 nanocomposite material by in-situ sol-gel process. Reliability of OLEDs encapsulated by the co-polyacrylate/SiO2 was also investigated in this part of study so as to evaluate its applicability to OLED packaging.
Experimental results revealed that the surfactant synthesis generated five different products. The products containing nitrogen atoms can be acidified and serve as the surfactants to intercalate into clay galleries. It was found that the synthesized surfactants may replace 71.4% of cations in clay lamellas and consequently form the acrylateclays. They effectively enlarged the d-spacing of clay lamellas from 13.6 to 33.2Å according to XRD analysis. The DTG analysis showed that the methylacrylate groups in the synthesized surfactants may react with acrylate/methylacrylate groups in monomers via photo-polymerization process. The photo-crosslinking subsequently promoted the compatibility between organic/inorganic portions. Such an effect led to the formation of nano-scale clay segments with thickness about 60 to 80 nm in co-polyacrylate/acrylateclays resin sample and an intercalated clay structure in epoxide/acrylateclays resin sample, as revealed by the TEM observation. The 5% weight loss temperature (Td) of co-polyacrylate/acrylateclays nanocomposite material was increased up to 16�aC when 5 wt.% of clay was added. The average optical transmittance of co-polyacrylate/acrylateclays resin sample reduced from 88.7% to 76.6% in visible-light wavelength range and the moisture absorption decreased from 3.44% to 1.31%. For epoxide/acrylateclays nanocomposite resin containing 5 wt.% intercalated segments, the Td increased from 149 to 213�aC, the coefficient of thermal expansion (CTE) reduced from 228.9 ppm/�aC to 80.5 ppm/�aC, the average optical transmittance slightly reduced from 86.0% to 83.7%, the moisture absorption decreased from 12.70% to 6.12% and the adhesion strength remained 43.8 kgf/cm2. For the epoxide/acrylateclays nanocomposite applied to OLED packaging, the lifetime of nanocomposite-sealed OLED is two-fold higher than that of acrylate resin-sealed OLEDs. The intercalated clay structure could sufficiently increase the permeation path of moisture, subsequently retarded the degradation of OLEDs.
For the photo-curable co-polyacrylate/silica nanocomposite resin containing 10 wt.% nano-sized silica particles, the glass transition temperature (Tg) ascended from 86�aC to 107�aC, the CTE decreased from 99.2 ppm/�aC to 30.6 ppm/�aC, the Td remained 180�aC, the moisture permeability reduced from 13.59 g/m2��24 hrs to 10.41 g/m2��24 hrs, the Young’s modules increased from 9.5 GPa to 265.8 GPa, the adhesion strength improved from 20.2 kgf/cm2 to 42.8 kgf/cm2 and the average optical transmittance changed from 82.3% to 82.0%; besides, at 10 kV/cm its leakage current density greatly diminished from 235 nA/cm2 to 1.3 nA/cm2, the dielectric constant was as low as 3.93 and the tangent loss was 0.0472. By applying co-polyacrylate/silica nanocomposite resin to direct encapsulation of bottom-emitted OLEDs, it found that the curing process did not affect the luminance of encapsulated devices and the device driving voltage decreased from 6.77V to 6.09V due to improved insulation property. Moreover, the lifetime of nanocomposite-encapsulated OLED increased from 178 hrs for resin-encapsulated OLED to 350 hrs for nanocomposite-encapsulated OLED. Experimental analyses indicated that excess UV irradiation may degrade the physical properties of nanocomposite resin such as insulation property and thermal resistance so as to deteriorate the lifetime of devices.
Finally, above studies indicate that the dispersion of inorganic fillers and adhesion properties of nanocomposite sealing resins played important roles on the reliability of OLEDs.
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