層與層自組裝奈米複合阻氣薄膜之交聯與阻氣機制研究

Abstract

本篇論文探討交聯反應對分支聚乙烯亞胺及蒙脫土所製作的層與層自組裝奈米複合薄膜對阻氣性質的影響，主要目的為減低薄膜本身的吸濕性質以及改善阻絕水氣的性質。首先調控製程參數來最佳化未交聯的奈米複合薄膜製程，包含分支聚乙烯胺的分子量、溶液濃度和酸鹼度。此製程採用分支聚乙烯胺分子量為25000、溶液濃度為0.1 wt% 和pH=10 時擁有規則排列的蒙脫土結構、低氣體滲透率和優越的光穿透度。有三種交聯劑被用來交聯層與層奈米複合薄膜，包含戊二醛、己二酸和乙二酸。不同於文獻所報導交聯劑對層與層自組裝奈米複合薄膜產生的效應，我們發現交聯劑造成薄膜的膨潤現象而非使奈米複合薄膜變緊密，且氣體滲透率明顯的上升。此現象歸因於交聯劑膨潤分支聚乙烯胺相，造成片狀的蒙脫土排列混亂因而創造出快速的氣體穿透路徑穿透過薄膜。我們的研究發現指出，這種利用交聯劑去改善層與層自組裝奈米複合薄膜的方法是無法達成目的的，利用高分子本身具有帶電性質以及可交聯的官能基可能是可行的解決方法。

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.