以原位聚合製備高阻氣性環氧樹脂/石墨烯複合材料

Abstract

由於石墨烯具有不透性、疏水性和非常大的長寬比等獨特優勢，石墨烯/高分子奈米複合材料成為一種很有前途的封裝材料，可滿足敏感性電子產品所需的阻氣要求，然而石墨烯/高分子奈米複合材料的發展一直受到限制，因為石墨烯之間擁有很強的內聚力，使其難以均勻分散在高分子基質中。本研究開發了能夠均勻分散高濃度且具有大長寬比的石墨烯的無溶劑環氧樹脂配方，再利用原位聚合製備出高阻水氣性質的複合材料。藉由測試一系列含有對石墨烯高親和性結構的環氧樹脂單體，找出有最佳的分散能力的單體，其中雙酚 A 二縮水甘油醚（DGEBA-377, Mn ~ 377）和雙酚 A 丙氧基化二縮水甘油醚（BPDG）因為含有苯環結構，因此具有很好的石墨烯分散性，最後再添加二亞乙基三胺 (DETA) 硬化劑來將石墨烯/環氧樹脂單體混合物固化。根據實驗結果，與純高分子膜相比，加入石墨烯後的高分子複合材料薄膜水氣滲透速率(WVTR)下降98.3%，遠比過去關於石墨烯/高分子之阻水氣的相關文獻還多。另外，我們發現在環氧樹脂單體中加入微量聚乙烯吡咯烷酮 (PVP) 作為分散穩定劑 (DSA) 可使石墨烯分散性進一步提升，DGEBA-377/DETA/PVP 配方因具有大量的苯基再加上 PVP 的 DSA 效應增強了石墨烯的分散性，相較未加入石墨烯的薄膜，阻氣性達到了前所未有的提升，WVTR 下降比例大於 99.5%，而在DSC的分析中發現添加石墨烯後，材料的玻璃轉移溫度(Tg)提高了，這是因為石墨烯片在基質中的侷限效應(confinement effects)限制了高分子鏈的移動。根據實驗結果，我們證明了一種非常有前景的方法來製備高性能且無溶劑的高分子密封劑，能夠應用於電子元件或其他產品。

Graphene/polymer nanocomposites are a promising type of encapsulant material for achieving high moisture/gas-barrier performance required for sensitive electronic devices, thanks to graphene’s unique advantages of impermeability, hydrophobicity, and large aspect ratio. However, development of graphene/polymer nanocomposites has been impeded by graphene’s resistance to dispersing in a polymer matrix due to its exceptionally strong cohesive forces. This study developed solvent-less epoxy precursor formulations capable of uniformly dispersing high concentrations of pristine, non-oxidized, and large-aspect-ratio graphene, which allowed facile fabrication of graphene/epoxy polymer nanocomposite films with excellent moisture-barrier properties via in-situ polymerization. By testing a range of epoxy precursors containing structural moieties with potentially high affinity to graphene, bisphenol A diglycidyl ether (average molecular weight ~377) (DGEBA-377) and bisphenol A propoxylate diglycidyl ether (BPDG) were identified as possessing high graphene dispersibility. Facile in-situ polymerization of the graphene/epoxy precursor mixtures was achieved by the addition of diethylenetriamine (DETA) as a hardener. The graphene dispersibility of the precursor formulations was found to further improved upon the introduction of a trace amount of polyvinylpyrrolidone (PVP) to serve as a dispersion-stabilizing agent (DSA). The nanocomposite films upon optimization of their graphene content exhibited fractional WVTR reductions of > 98.3% compared with the unreinforced epoxy polymers, which were on par or far superior to literature results on graphene/polymer nanocomposite moisture-barrier films. Notably, the DGEBA-377/DETA/PVP formulation achieved an unprecedented level of fractional WVTR reduction at > 99.5% owing to its enhanced graphene dispersibility as a result of its abundance of phenyl moieties as well as the DSA effects of PVP. DSC analyses revealed that the Tg‘s of the nanocomposites were distinctly elevated relative to their unreinforced polymer matrices, which was attributed to the confinement effects of the graphene reinforcements. Our results demonstrate a highly promising approach to fabricating high-performance, solvent-less, polymer-based encapsulants for electronics and other applications.