二氧化矽/聚二甲基矽氧烷複合薄膜微結構與滲透蒸發效能之實驗與分子動態模擬解析

Micro-structures and Pervaporation performance of Silica/PDMS Mixed-Matrix Membrane: Experimental and Molecular Dynamics Simulation Studies.

李福志(Fu-Chih Li)

指導教授 ： 陳昱劭 ； 童國倫

中原大學/工學院/化學工程研究所/碩士(2014年)

https://doi.org/10.6840/cycu201400615

摘要

本研究主要發展具有潛力與高分離效能的二氧化矽/聚二甲基矽氧烷複合薄膜，將其應用於於5 wt% 的乙醇水溶液滲透蒸發分離，並且利用分子動態模擬技術解析添加入聚二甲基矽氧烷高分子薄膜中的二氧化矽的微結構以及小分子在網狀結構中的輸送行為。藉由添加二氧化矽網狀結構於聚二甲基矽氧烷(poly-dimethylsiloxane, PDMS) 高分子薄膜內，製備出二氧化矽/聚二甲基矽氧烷複合薄膜 (mixed matrix membranes, MMMs)，其中添加入高分子薄膜中的二氧化矽網狀結構為矽酸四乙酯 (Tetraethyl orthosilicate, TEOS) 前驅物與1,2-雙(三乙氧基硅基)乙烷 (1,2-Bis(triethoxysilyl)ethane, BTESE) 前驅物，經由水解與縮和兩步驟所形成的二氧化矽網狀結構。將此薄膜應用於5 wt%的乙醇水溶液滲透蒸發分離，其中添加二氧化矽網狀結構時，使得聚二甲基矽氧烷薄膜中具有額外的孔洞可以讓小分子進行透過；由於BTESE具有較長的Si-C-C-Si片段，使得整個網狀結構擴張，進而顯示出較大的孔洞讓小分子進行透過行為，因此，BTESE/PDMS的複合薄膜在乙醇與水的滲透蒸發分離程序中具有較高的通量。同時， Si-C-C-Si片段也是屬於較疏水的鏈段，當薄膜結構中存在著Si-C-C-Si片段時，提升了薄膜表面的疏水特性；另一方面，於聚二甲基矽氧烷薄膜中添加二氧化矽網狀結構，可以有效地抑制薄膜的澎潤，進而顯示出較高的乙醇與水透過選擇比。本研究主要以分子動態模擬 (molecular dynamics, MD) 技術分析非均相的二氧化矽網結構特性與小分子輸送行為。在結構特性部分，本研究以自由孔隙、容通孔隙與孔徑分佈解析二氧化矽結構，發現由於 BTESE 的二氧化矽網狀結構中具有較長的Si-C-C-Si 片段，可以有效地使結構擴張，讓結構中在小孔洞區域中的數量減少，而在大孔洞區域中的數量明顯增加，且薄膜結構中可以讓小分子輸送的有效體積是有明顯的增加。另一方面，本研究亦利用小分子在二氧化矽網狀結構中的擴散係數以及溶解度參數解析水分子與乙醇分子的吸附以及擴散行為，發現由於 BTESE 的二氧化矽網狀結構中具有較多的有效體積以及較大的孔洞，使得小分子在其網狀結構中的移動性較高；另一方面，BTESE的二氧化矽結構中，由於其具有疏水的 Si-C-C-Si 片段，因此使得水分子不易吸附於其網狀結構中。冀以此理論模擬概念測定與預測材料以及分析非均相的二氧化矽網結構，作為滲透蒸發薄膜之材料設計參考。

關鍵字

陶瓷薄膜 ； 二氧化矽/聚二甲基矽氧烷複合薄膜 ； 滲透蒸發 ； 分子動態模擬。

並列摘要

The development of potential membrane with high separation performance aims to separate the 5 wt% of ethanol and analyze the micro-structure and small molecules transport behaviors of membrane via molecular dynamic (MD) simulation. The mixed matrix membranes (MMMs) with Polydimethylsiloxane (PDMS) as basis is prepared on the ceramic substrate and added the inorganic materials such as Tetraethyl Orthosilicate (TEOS) and 1,2 bis (triethoxysilyl) ethane (BTESE) into the polymer. This membrane is applied to separate the 5 wt% of ethanol solution. Adding the silica network into the PDMS membrane forms the extra pores for small molecules to transport so the flux increased with the silica content increased. Due to the larger Si-C-C-Si segments, the BTESE network was expand and possessed the lager pores for small molecules to transport. As a result, the BTESE/PDMS MMMs show the higher flux during the pervaporation process with the 5 wt% of ethanol solution. On the other hand, the BTESE/PDMS MMMs also showed the higher separation factor due to the hydrophobic Si-C-C-Si segments that formed the more hydrophobic surface on the membrane. Adding the silica network into the PDMS membrane could constrain the swelling effect of membrane so that the separation factor increased. The characteristics of the TEOS and BTESE silica network was analyzed via molecular dynamic simulation. The micro-structure was investigated with fractional free cavity (FFC), fractional accessible cavity (FAC) and cavity size distribution (CSD). Due to the existence of Si-C-C-Si segments, it was found that the silica network was expanded and the effective cavity for small molecules to transport was increased. And then, the small molecules transport behaviors were estimated with the diffusivity and solubility. Because of the more effective and larger cavities, the small molecules possess higher mobility in the BTESE silica network. The Si-C-C-Si segments are also hydrophobic segments so the water molecules are hard to load on the BTESE silica network. The computer simulations are used in not only the qualitative analysis but also quantitative analysis of materials so that reducing the human power and nature resource. The molecular dynamic simulation technique proved to be a promising tool for material development and analyze the amorphous silica network on a micro scale.

並列關鍵字

Pervaporation ； Molecular Dynamic Simulation. ； Ceramic membrane ； Silica/PDMS Mixed-Matrix Membranes

參考文獻

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