Determining zeta potential of membrane pores by electroosmosis and streaming potential methods

• Main Authors: Wei-Yi Tso, 左煒憶
• Other Authors: CJChuang
• Format: Others
• Language: zh-TW
• Published: 2001
• Online Access: http://ndltd.ncl.edu.tw/handle/60407057697720433198

碩士 === 中原大學 === 化學工程研究所 === 89 === 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. .