國合計畫：非溶劑蒸氣誘導式相分離之探討

Abstract

本計畫利用水蒸氣來誘導高分子鑄膜液進行相分離，進而成膜。研究中探討 poly(etherimide)(PEI)及poly(methyl methacrylate)(PMMA)兩種高分子溶於NMP 溶劑中， 在相對濕度70 ％環境下的成膜過程。先利用重量量測來初步分析成膜過程中水蒸氣被吸 入高分子溶液之過程，並進一步利用confocal Raman spectroscopy(在法國進行)及FT-IR microscopy(在台灣進行)來分析局部的濃度變化。結果顯示蒸氣誘導之成膜過程可描述如 下：由於NMP 與水蒸氣的高度親和性，NMP 會向界面移動並將水吸入薄膜;NMP 的移 動會導致高分子濃度梯度產生(界面較低而底部較高)，故成膜後表面孔隙度會較膜底部 大;在水進入鑄膜液中而導致相分離產生後，由於高分子富相的膠結作用，水吸至鑄膜液 表面的速度會比進入鑄膜液為快，導致表面形成一層液體層。對PEI 的系統，我們可成 功定量分析成膜過程中高分子、溶劑及非溶劑的濃度變化，並可在相圖上定出成膜路徑， 此成果在高分子成膜領域中，未曾有相關的文獻報導，係屬首創。

PEI (polyetherimide) and PMMA(poly methyl methacrylate) membranes were prepared by coagulation in humid air with a relative humidity of about 70%. Gravimetric measurements were performed first to analyze the amount of water drawn into casting solution during the forming of membranes. To get insight into the local concentration change during membrane formation, two advanced instruments were used, confocal Raman spectroscopy (in France) and FTIR microscopy (in Taiwan). The results from membrane structure, confocal Raman, and FTIR microscopy suggest the membrane forming process be described as follows: NMP migrates to the surface of casting film and draws water to the casting film due to high affinity of NMP for water; the migration of NMP towards interface results in a polymer concentration gradient across the casting film, with lower concentration near the surface, which can well correlate with the pore size distribution across the membrane; the gelation of the polymer-rich phase after phase separation would reduce the water permeation rate through the casting film and generates a liquid layer on top of the casting film because the hold up of water. For the PEI system, we can analyze quantitatively the concentration of polymer, solvent and nonsolvent and determine the composition paths in the ternary phase diagram, which has never been reported before in the literature.