原位聚合之壓克力/石墨烯複合材料之阻氣性質研究

Abstract

高分子由於其低成本和易於加工性而成為最被廣泛使用的阻氣材料之一，但由於高分子的高水氣穿透率，高分子阻氣膜在封裝對水氣敏感的電子元件上的應用會受到很大限制。石墨烯是一種能阻氣性佳的二維材料，因此非常適合與高分子混參，能大幅降低石墨烯/高分子複合材料的水氣穿透率。然而在高分子中均勻分散足量的石墨烯是難以達成的，因此低水氣穿透率的石墨烯/高分子複合材料並不容易製備。本研究為了增進石墨烯的分散性以製備出低水氣穿透率的阻氣膜，首先藉由表面張力的匹配篩選出五種壓克力單體，進行分散性測試以找出分散石墨烯能力最好的壓克力單體。結果發現含有苯基的壓克力單體有較好的分散性，能形成高濃度的石墨烯分散液，尤其是乙氧基化雙酚A二丙烯酸酯（ethoxylated bisphenol-A diacrylate, EBAD）能分散最高濃度的石墨烯。因為在所選的單體中，EBAD上有大量的苯基，能與石墨烯有最好的親和性。接著我們採用溶劑置換法進一步提高了石墨烯在EBAD中的分散濃度。首先將石墨烯分散在已知的好溶劑──N-乙烯基-2-吡咯烷酮（N-vinyl-2-pyrrolidone, NVP）中，然後再交換到EBAD單體中。經過溶劑置換後，石墨烯能更均勻的分散在EBAD中。接著使用光起始劑（2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-芐基-2-二甲基氨基-1-（4-嗎啉苯基）-丁酮-1）和熱起始劑（2,2′-Azobis (2-methylpropionitrile), 偶氮二異丁腈）去原位聚合石墨烯/EBAD。結果顯示光起始劑並不能固化石墨烯/EBAD複合膜，因為石墨烯會吸收大量的光源，阻礙光起始劑的分解。最後我們藉由熱聚合置備出了石墨烯/EBAD複合阻氣膜並最佳化石墨烯濃度，含有1.4 wt%的石墨烯阻氣膜有最低的水氣穿透率（7 × 10-2 g/m2·day），相較未加入石墨烯的高分子膜，水氣穿透率達到了前所未有的下降幅度，超過99.5%。同時此複合阻氣膜的熱分解溫度提升了28 ℃。此研究透過溶劑交換的方法提升了石墨烯在EBAD中的分散性，並用原位聚合法成功置備出高阻氣性、高熱穩定性且易於加工的石墨烯/壓克力複合薄膜。

Polymers are the most widely used type of gas-barrier materials thanks to their low costs and ease of processing, but their application to sensitive electronic devices has been limited by their high gas permeability. Graphene, a two-dimensional structure that is impermeable to gases, has been identified as a promising filler to decrease the water vapor transmission rate (WVTR) of its polymer matrix by orders of magnitude. However, such a drastic reduction in WVTR from graphene/polymer composites has not been achieved due to the difficulty of uniformly dispersing a sufficient amount of graphene in most polymers. This study addresses this issue with a two-pronged approach: (1) identify acrylate monomers that are good solvents of graphene through matching of surface tensions and actual dissolution experiments; (2) improve the dispersibility of graphene in the identified monomers through a solvent exchange method, where graphene was first dispersed in a good solvent which was then exchanged with the monomers. Of five acrylate monomers tested, ethoxylated bisphenol-A diacrylate (EBAD) showed the highest dispersibility of graphene thanks to its abundant phenyl substituents providing high affinity with graphene. Solvent-exchanging with N-vinyl-2-pyrrolidone (NVP) further increased the dispersibility of graphene in EBAD. Curing of the graphene/EBAD dispersion was examined with a photo initiator [2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1] or a thermal initiator [2,2′-Azobis (2-methylpropionitrile)], of which the photo initiator was found unusable because its initiation was hindered by the graphene phase, which strongly absorbed the incident light. The thermally cured graphene/EBAD composite with an optimized 1.4 wt% of graphene exhibited a > 99.5% reduction in WVTR over that of the poly-EBAD matrix—an unprecedented scale of reduction for reinforced polymers, reaching a WVTR of 7 × 10-2 g/m2·day. Additionally, the thermal decomposition temperature of the composite film was raised by 28 °C from that of the poly-EBAD. The combination of high gas-barrier performance, thermal stability, and processability of the graphene/EBAD composite film offers a practical solution for the packaging of sensitive electronics.