殘留溶劑對含氟聚亞醯胺薄膜自由體積與 分離效能影響之分子模擬

Residual Solvent Effect on Free Volume and Performance of Fluorinated Polyimide Membrane: A Molecular Simulation Study

張楷焄(Kai-Shiun Chang)

指導教授 ： 童國倫

中原大學/工學院/化學工程研究所/碩士(2006年)

https://doi.org/10.6840/cycu200600451

摘要

本研究以分子模擬技術研究殘留溶劑對含氟聚亞醯胺薄膜(6FDA-mPDA PI membrane)之自由體積與分離效能影響。首先，以分子力學原理建立結構穩定的薄膜分子模型。確認分子模型適用於分析殘留溶劑效應後，以分子動態模擬(molecular dynamics simulation, MD)方式進行動態計算分析，隨後並以蒙地卡羅法(Monte Carlo method, MC)分析氣體吸附行為。
在本研究中，可由分子力學(molecular mechanics, MM )原理建構的薄膜模型，經由氣體吸附係數計算，明顯表現出殘留溶劑對6FDA-mPDA PI薄膜的影響。進行MD動態計算後，由高分子構形分析發現，鑄膜溶劑與對高分子結構並無影響，主要仍以6FDA-mPDA PI本身特性為主；由能量分析中顯示，殘留溶劑分子可增進高分子鏈的擾動特性，利於提升高分子鏈易曲性；在自由體積分析中顯示，溶劑殘留量多寡改變薄膜內自由體積分佈，進而提升有效自由體積分率。
在氣體吸附行為討論中，由定量分析發現，殘留溶劑量明顯影響氣體吸附能力；而定性分析顯示，自由體積分佈決定氣體吸附位置。比較自由體積後顯示，殘留溶劑離開薄膜後，所釋放的自由體積控制氣體吸附量。當溶劑分子釋放之自由體積不大時，則薄膜與氣體、溶劑分子間作用力和氣體與薄膜間吸附能影響氣體吸附能力。比較不同壓力下的氣體吸附能力發現，壓力增加會導致殘留溶劑對氣體吸附能力影響降低。針對氣體熱運動機制分析，顯示含殘留溶劑分子會略微提升氣體有效熱運動機率，但影響程度不高，推測殘留溶劑對氣體擴散機制無明顯影響。
由以上結果顯示，在高分子特性方面，殘留溶劑主要影響高分子易曲性；在薄膜形態方面，殘留溶劑改變有效自由體積分佈，進而影響氣體吸附能力；在氣體透過現象方面，殘留溶劑效應主要影響氣體吸附行為。

關鍵字

氣體分離 ； 殘留溶劑 ； 自由體積 ； 分子動態模擬

並列摘要

Residual solvent effect on free volume and performance of fluorinated polyimide membrane (6FDA-mPDA PI membrane) was investigated in this study by a molecular simulation technique. In the first, the stable structure in the molecular model was built under a molecular mechanic theory. The dynamic calculation and analysis through a molecular dynamic simulation (MD) were carried out after validating the molecular model with suitable characteristics for analyzing the residual solvent effect. And then the gas sorption behavior was discussed through the Monte Carlo method.
In this study, the residual solvent effect on the membrane model which was built under a molecular mechanic theory, could be revealed clearly having calculated the gas sorption coefficients. After the MD calculation, it could be found that the polymer structure of PI membrane would not be affected by the casting solvent. At the same time, it was shown that the polymer properties were decided mainly from the characteristics of 6FDA-mPDA PI. The fluctuation and flexibility of polymer chains were influenced by residual solvent molecules under the energy analysis. The free volume distribution analysis revealed that the free volume distribution in the membrane was changed by the amount of residual solvent, and then the effective fractional free volume was also improved.
In the discussion of gas sorption behavior, it was found that the gas sorption ability was affected by the quantity of residual solvent under the quantitative analysis. Moreover, it was revealed that the gas sorption sites depended on the free volume distribution under the qualitative analysis. After comparing with the free volume, it was exhibited that the gas sorption loading was controlled by the free volume released resulting from the solvent left the membrane. When the free volume was released rarely as residual solvent molecules left, the gas sorption ability was both influenced by the interaction among membrane molecules, gas molecules, solvent molecules and the sorption energy between gas molecules and membrane molecules. Comparing with the gas sorption ability under different pressures, it was found that the residual solvent effect on gas sorption would be reduced at higher operating pressure. From the analysis of the thermal motion of gas molecules, it was found that the effective thermal motion of gas molecules was improved slightly as residual solvent molecules remained in the membrane matrix. However, the extent of residual solvent effect was found to be very little on gas thermal motion. As a result, it was inferred that residual solvent had no obvious influence on gas diffusion mechanism.
For the results, we mentioned above, the flexibility of polymer was regarded as a main influencing factor resulted from residual solvent effect on polymer property. On the other hand, the effective free volume distribution was changed by residual solvent influencing the gas sorption ability of the membrane. In addition to that, it was considered that the gas sorption behavior was the main criteria caused by residual solvent on gas transport phenomena.

並列關鍵字

Residual Solvent ； Free Volume ； Gas Separation ； Molecular Dynamics

參考文獻

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