電漿聚合有機矽氧膜之孔洞結構控制於氣體分離應用

Control of pore structure in plasma-polymerized SiOCH films for gas separation

羅嘉豪(Chia-Hao Lo)

指導教授 ： ARRAY(0xacaa500)

中原大學/工學院/化學工程研究所/博士(2010年)

https://doi.org/10.6840/cycu201000951

摘要

氣體分離程序中，製備出具有高交聯度結構的透過選擇層及多孔性基材層之複合薄膜，被認定為可提升其氣體透過率並保有原先高選擇性之方法。由於電漿聚合有機矽氧薄膜(SiOCH)擁有緻密結構及可控制之交聯度等特性，其中交聯度的控制可藉由電漿參數(如電漿功率、單體流率、系統壓力等)調整，因此被認為是合適的氣體分離膜，然而SiOCH薄膜非常薄，造成鑑定其內部孔洞大小及分布的困難，特別是在不同深度下。
因此，本論文著重在利用有機矽氧烷單體，以電漿聚合方式沉積SiOCH薄膜於高分子基材上並控制其孔洞大小，最後利用正子煙滅圖譜結合慢速正子束技術分析SiOCH膜內微結構隨薄膜深度之變化。首先，有必要了解正子於不同材料內之煙滅行為，例如有機、無機及有機無機混合材料。實驗結果發現，藉由電漿頻率的調整，SiOCH薄膜型態可分別呈現平整及超疏水表面於13.56 MHz及40 kHz。對於平整SiOCH薄膜而言，基材膜種類、單體化學結構以及電漿功率為影響其孔洞結構之最主要因素，由正子技術分析得知，SiOCH薄膜於多孔性基材上呈現出整體及過度層結構，而多孔的基材表面致使過度層厚度增長且為高孔隙度，因此展現高氣體透過率。當使用具有環狀結構之單體時，隨著電漿功率的增強，使得環狀結構開環的機會增加且導致大孔洞的產生。而針對超疏水膜製備而言，當系統總壓力高於0.6 mbar時，電漿中氣相成核反應會增強進而導致顆粒狀的SiOCH膜生成，其表面呈現大於160o的對水接觸角及僅2o之對水接觸角遲滯效應，實驗中發現，SiOCH薄膜表面碳氫基團及微結構的保留是提升超疏水特性之重要因素。

關鍵字

PECVD ； SiOCH薄膜 ； 氣體分離膜 ； 超疏水表面 ； 正子煙滅 ； 孔洞結構

並列摘要

In gas separation, the fabrication of composite membranes consisting of a permselective thin top layer with high cross-linking structures and a porous substrate has been regarded as a solution for improving gas permeability and simultaneously retaining high selectivity. A plasma-polymerized SiOCH film has been known as an appropriate gas separation membrane because it possesses a dense structure, the crosslinking degree of which could be controlled by adjusting plasma parameters such as plasma power, monomer flow rate, and system pressure. However, the pore size and distribution in SiOCH films, especially in the region of depth profile, are difficult to measure by conventional techniques because of they are very thin.
This thesis is concerned with the control of pore structure in a plasma-polymerized SiOCH film on a polymeric substrate by using an organosilicon source. The positron annihilation spectroscopy (PAS) coupled to the slow positron beam technique was used to identify the microstructure of SiOCH films as a function of depth. This step required to have a good understanding of the positron annihilation characteristics of different materials such as organic, inorganic, and hybrid materials. Depending on plasma frequency adjustments, SiOCH films with a flat and a superhydrophobic (SHP) surface were fabricated at 13.56 MHz and 40 kHz, respectively. For a flat SiOCH film, substrate type, chemical structure of precursor, and RF power were the major variables that influenced the pore structure. When SiOCH films composed of two layers (bulk and transitions layers) were deposited on porous substrates, they displayed a long transition layer based on the PAS analysis and possessed a high gas permeability due to the surface porosity of the substrate. When the precursor used possessed a cyclic ring structure, an opportunity of a break-up of the cyclic ring would increase with increasing RF power and then induce formation of new big pores. For the preparation of SHP films, when the total pressure was higher than 0.6 mbar, the gas nucleation reaction was enhanced to induce roughness on SiOCH films, and it would show a high WCA of over 160° and a low WCAH of only 2 degrees. Both the hydrocarbon preservation and microstructure were the main factors in improving the surface superhydrophobicity of SiOCH films.

並列關鍵字

positron annihilation ； pore structure ； gas separation membranes ； SiOCH films ； PECVD ； superhydrophobic surface

參考文獻

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