- 學位論文
以電滲透及流線電位決定薄膜之膜孔界達電位
Determining zeta potential of membrane pores by electroosmosis and streaming potential methods
摘要
摘要 膜過濾所遭遇的最大困擾是膜結垢所導致之濾速嚴重衰減及穿透選擇性下降等，除膜面上流體流動機構、膜材親水性與膜孔徑等因素會影響膜結垢之行為與程度外，膜材電荷亦在膜分離中扮演重要的角色，膜電荷是決定欲過濾物質與膜面相互作用力之主要變數，而若於過濾操作時外加電場，膜電滲透（有時影響濾速甚鉅）亦取決於膜孔電性及電荷量，由此可見膜電荷對膜分離效能有決定性的影響。 為了解膜孔界達電位與膜電動現象之關係，本研究首先建立含非對稱孔徑薄膜之電滲透及流線電位等電動方程式，探討膜孔對稱性、電雙層重疊及兩層複合膜各層之物理化學特性等對電滲透與流線電位等的影響，並提出了Helmholtz-Smocholowski模式的修正因子，結果顯示對非對稱膜孔其電滲透及流線電位之Helmholtz-Smocholowski方程式的修正因子皆相同，對於含兩層之複合膜，其緻密層與多孔層兩者在電滲透流率貢獻度之比例上與在流線電位方面比例是相同的。若忽略兩不同膜層之電導度的差異，在離子濃度較大，膜孔內電雙層效應較小時，緻密層的電滲透作用對整體電滲透流速有較大的影響而流線電位的結果亦是。 在實驗方面，建立了薄膜電動量測實驗系統，並進行0.2μm（含對稱與非對稱兩組）微過濾膜之量測，探討溶液離子濃度、膜孔對稱性、膜孔大小及BSA蛋白質過濾等對膜孔界達電位的影響。以0.2μm PC對稱膜浸置於KCl與NaCl溶液之結果顯示，其膜孔界達電位會隨離子濃度增加而減少。由電滲透與流線電位兩方法所決定之界達電位，在低離子濃度時差距相當大，但在高於0.01M則甚接近。以同材質但孔徑分別為0.05、0.1及0.2μm之PC膜的結果顯示，三者之電滲透流速很接近，流線電位的結果亦類似。三者由電滲透所得之界達電位有較大的差距；而由流線電位所得者則非常接近，但若考慮膜孔電導度，除最小膜孔外，其真實電位甚一致。 0.2μm PC膜經pH=4之 BSA溶液過濾後，其表觀界達電位有明顯的變化，而在pH=5接近蛋白質等電點時，過濾前後之膜電性變化則甚小，但若使用較小膜孔（0.05μm）過濾相同體積之BSA溶液後，於pH=5時過濾前後界達電位有明顯變化，可能是因膜孔較小，可阻擋或吸附較多的蛋白質於膜孔中，使膜孔內電雙層的分佈明顯改變所致。
並列摘要
ABSTRACT It has been recognized that the electric charge of membranes play an important role in the performance of membrane separations, since the electrochemical properties of the membrane exert profound influence on the nature and magnitude of the interaction between the membrane and the charged particle in solutions, thus affecting the filtration rate and the selectivity of the membrane. For the reason, there is much interest in characterizing the charge of the membrane. In this study, a theoretical analysis to relate the electroosmotic flow rate and streaming potential with the zeta potential and the structure of asymmetric membranes was presented, and then experiments were performed to investigate the effects of electrolyte concentration and the filtration of BSA solutions on the zeta potential of the symmetric PC and asymmetric nylon membranes. Theoretical results showed that the correction factors for the streaming potential and the electroosmosis in the one–layer membrane with pore sizes varying along the axial direction are not only the same but also independent of the fluid flow direction in the membrane. For the two-layer composite membranes, each layer(skin and supported) was modeled as a bundle of identical capillary tubes, the contribution of the each layer to the global streaming potential of the membrane is the same as that to the global electroosmosis. It was shown that the domination of skin layer to the global electrokinetic phenomena of the membrane decreases with the decreasing of electrolyte concentration if the ratio of zeta potential between the two layer is independent of the electrolyte concentration. It appeared that the zeta potential of symmetric PC membranes evaluated from streaming potential technique is similar to that by electroosmosis except at low salt concentration. However, the apparent zeta potential of the asymmetric nylon membrane is strongly dependent on the determining techniques and the electric field direction. Experimental results showed that the differences in electrokinetic behavior between the clean and the fouled (after filtering BSA solution) membrane is significantly affected by the pH of the solution and the pore size of membranes, at the pH near BSA isoelectric point and with larger pore sizes the difference is very small. .