研究以濕式相轉化法抑制聚碸膜其巨型孔洞的形成

巨型孔洞在薄膜中的表現雖然意味著多孔的結構，但同樣的它卻被認為是膜的弱點。這些巨型孔洞很容易受外力影響而改變其原有結構，隨著使用時間的增長，最終可能會導致薄膜過濾性能變差。本研究對於在鑄膜液中加入水作為添加劑以抑制聚碸膜中巨型孔洞形成的效果作探討。我們發現在聚碸膜的橫截面圖像中顯示，透過添加水的條件成功抑制了巨型孔洞的生成，我們認為這個結果歸因於鑄膜液中黏度的增加，導致質傳動力減慢，從而影響溶液的分層。此外，透過觀察鑄膜液的流變行為發現，高度的鏈纏結有助於減少巨型孔洞的形成。使用 2P 作為 PSf 的溶劑會使鑄模液具有高黏度性並且保留孔洞之間有互聯的特性，從而防止粗化。經由添加劑的加入，有效地抑制了巨型孔洞，同時又能保持PSf 膜的高孔隙率 (88% ~ 76%) 和平均孔洞大小 (0.65µm ~ 0.3µm)不變。這也通過測量及未添加水的聚碸膜純水通量結果相仿得到證實。添加水後的聚碸膜提高了楊氏模量，證明膜的機械特性獲得顯著改善。最後經由SEM拍攝將此研究套用在其他系統（PSf/NMP 和 PSf/DMAc）的圖像中顯示出類似趨勢，進一步驗證了利用水作為添加劑來消除巨型孔洞生長的可行性。這些結果表明，以水作為鑄膜液添加劑可以提供一種簡單且極具成本效益的策略來獲得無巨型孔洞的聚碸膜。

關鍵字

非溶劑誘導式相分離；聚碸膜；添加劑；黏度；巨型孔洞

並列摘要

Macrovoids, although imply a porous substructure, are considered weak points in membranes. They are prone to compaction which could eventually lead to poor filtration performance over time. In this study, we studied the effect of using water as an additive in the casting solution to help suppress the formation of macrovoids in polysulfone membranes. The cross-section images of the membranes exhibited the successful suppression of macrovoids which can be attributed to the enhancement of the solution viscosity causing the mass transfer kinetics to be slowed down, consequently affecting the demixing of the solution. Moreover, the rheological behavior of the casting solutions revealed that high degree of chain entanglement helped mitigate macrovoid formation. Using 2P as the solvent for PSf permitted the retention of interconnected pores due to the high viscosity of the solution which prevented coarsening. The high porosity ranges from 88% to 76% and large pores 0.65µm to 0.30µm of the PSf membranes were still maintained, while the macrovoids were effectively suppressed by the incorporation of the additive. This was also verified by the similar measured pure water flux of the pristine and modified membranes. The mechanical attributes of the membranes were significantly improved as evidenced by enhancement of the Young’s modulus of the modified membranes. The feasibility of utilizing water as an additive to eliminate macrovoid growth was further validated when applied to other systems (PSf/NMP and PSf/DMAc) which showed similar trends in the SEM images. These results imply that water as a casting solution additive can provide a highly cost-effective and simple strategy to obtain macrovoid-free polysulfone membranes.