| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 100 === This study investigates effects of cross-linking on the gas-barrier property of branched polyethyleneimine (BPEI) / montmorillonite (MMT) nano-composite films prepared by layer-by-layer (LbL) self-assembly, with the goal of reducing the hygroscopic nature of the films and improving their moisture-barrier performance. The process for fabricating before-cross-linking nano-composite films was first optimized by tuning processing parameters including molecular weight of BPEI, concentration and pH value of the BPEI solutions. It was determined that a BPEI molecular weight of 25000, a concentration of 0.1 wt%, and a pH value of 10 resulted in a regularly aligned MMT, low gas permeability and excellent optical transparancy. Three cross-linking agents were applied to the LbL nano-composite films, including glutaraldehyde (GA), adipic acid, and oxalic axid. Contrary to previous reports on the effects of these cross-linking agents on LbL BPEI / MMT nano-composite films, we found that the cross-linking agents caused swelling instead of densification of the nano-composite films, and the gas permeability of the films significantly increased. This was attributed to the cross-linking agents swelling the BPEI phase, causing disordering of the MMT platelets which in turns created fast permeation passageways through the films. Our findings indicate that the approach of using cross-linking agents to improve gas-barrier property of LbL nano-composite films may be implausible, and that use of polymer electrolytes with cross-linkable functional groups may be a possible solution.
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