| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 107 === 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.
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