Electrokinetic phenomena of poly(vinyl butyral) hollow fiber membranes in different electrolyte solutions

QI Jing(漆静), WANG Yong-qian(王永前), QIU Yun-ren(邱运仁)

(1. School of Chemistry and Chemical Engineering, Central South University, Changsha 410083, China;2. Key Laboratory of Resources Chemistry of Nonferrous of Ministry of Education(Central South University), Changsha 410083, China)

Abstract:The streaming potential of poly(vinyl butyral) (PVB) hollow fiber membrane was studied in different electrolyte solutions (including NaCl, KCl, CaCl₂ and MgCl₂), the effects of ionic strength, ion valence and pH value on the streaming potential (SP) of the membrane were investigated. The zeta potentials and surface charge densities of the membrane were estimated on the basis of Helmholtz-Smoluchowski equation and Gouy-Chapmann theory. The results show that the PVB membrane has a weak negative charge due to the specific adsorption of ions. Moreover, the streaming potential, the zeta potential and the surface charge density of the membrane depend strongly on the salt concentration and the type and valence of ions. The iso-electric point (IEP) of the PVB membrane is around 3.0 in the monovalent media (NaCl and KCl) and 3.5 in divalent electrolytes (CaCl₂ and MgCl₂). A few retentions were obtained for PVB membrane in low concentration solutions. This result verifies that the negative charged membrane surface can reject inorganic solutes by means of electrostatic repulsion effect even though the size of membrane pores is much larger than the size of salts.

Key words:streaming potential; zeta potential; poly(vinyl butyral); hollow fiber membrane