層與層自組裝之奈米複合阻氣薄膜研究

Abstract

本研究主要探討如何利用旋轉塗佈之層與層自組裝製備以高分子(BPEI)與蒙脫土(clay)為材料的奈米複合阻氣薄膜。由於傳統上，層與層自組裝主要以浸泡(dip)的方式執行，過程相當耗時，因此，本研究的目的為開發快速製備層與層自組裝阻氣薄膜的製程，同時希望利用旋轉塗佈製程中所特有的離心力，使蒙脫土能在高分子基材中有良好的排列，有效地延長氣體滲透路徑，藉此得到優異的阻氣薄膜。在此研究中，我們成功地以旋轉塗佈的方式在PET基板上覆蓋50-bilayer的層與層自組裝薄膜，並使PET基板的氦氣滲透率(HeTR)從521.1下降至7.4(c.c./m2 day)。而在本研究中我們探討兩個影響氦氣滲透率的主要因素，其一是蒙脫土懸浮液的濃度，其二為滴加蒙脫土懸浮液後的乾燥時間，此兩項因素皆必須調整至一個適中的值才可得到優異的阻氣薄膜。另外，我們對以旋轉塗佈製備的層與層自組裝阻氣薄膜進行基本特性的分析，我們發現此薄膜具備良好的光穿透度以及優異的可撓性，同時在SEM及AFM的觀察下可以看到膜脫土規整的水平排列。雖然我們製備的阻氣薄膜能有效阻擋氦氣的滲透，但因為所使用的材料皆是親水性的材料，因此阻水氣能力並不佳。但我們發現此薄膜在高溫高濕環境下存放後，重新在真空環境下量測氦氣滲透率可以恢復原有的阻氣水準。

This study uses spin-assisted layer-by-layer (SA-LBL) assembly process to deposit nano-composite gas barrier films of sodium montmorillonite (MMT) and branched polyethylenimine (BPEI). The objective is to establish a fast process for fabricating LBL gas barrier films with highly ordered structure and excellent barrier performance, which is evaluated in terms of helium transmission rate (HeTR) and oxygen transmission rate (OTR). By identifying and optimizing the key factors determining the helium barrier performance of the SA-LBL films, including the concentration of MMT and drying time after MMT deposition, we successfully obtained SA-LBL films with excellent barrier performance: 50 bilayers of SA-LBL films (188 nm) deposited on PET substrates reduced the HeTR from 521.1 of the bare substrates to 7.4 (c.c./m2 day), with the OTR reduced from ~10 to 0.13(c.c./m2 day). SEM, TEM and AFM analyses reveal ordered in-plane alignment of the MMT platelets in the SA-LBL films, which accounts for the good barrier performance of the films, as the aligned MMT platelets significantly increase the tortuosity and length of the pathways travelled by permeants. The SA-LBL films also display remarkable optical transparency and flexibility, thanks to the presence of the polymer interlayers. Despite the hydrophilicity of the MMT platelets and the polar BPEI, the barrier performance of the SA-LBL films remains stable in an accelerated aging environment with high humidity (90% RH) and elevated temperature (60 ºC). However, the SA-LBL films are ineffective as moisture barriers, with WVTR reaching 6.507. In our future work, we will examine low-polarity polymers in place of or in addition to BPEI to improve the moisture-barrier performance of the SA-LBL films.