STUDY OF ADSORPTION AND ION-EXCHANGE PROPERTIES OF SOME POROUS MEMBRANES

Adsorption of ions and ion-exchange properties of three different types of polymeric microfiltration membranes (with pore sizes of 0.1-8 mu m) were studied by measuring the streaming potential and transport numbers in different electrolyte concentrations. A completely computerized apparatus for the measuring of the streaming potential, allowing a fast and accurate determination of the streaming potential as well as the study of slow adsorption kinetics, was built. The transport number in the membrane was determined by measuring the electromotive force in a cell with transference. The rotating diffusion cen was employed to overcome the problem created by the polarization layers. The measured data were used to estimate the surface charge density and the pore radius of the membrane in the swollen state. Furthermore, an effort to study the protein adsorption by both methods was made. The results clearly show that chloride ions are adsorbed on the pore wall, creating cation-exchange properties for the membrane. However, owing to the large pore size, only in dilute electrolyte solutions (less than or equal to 10(-3) M) did the transport number in the membrane deviate from its value in water. The protein cytochrome c is evidently adsorbed by a hydrophobic interaction, increasing the number of charges on the pore wall. This behaviour indicates that only a monolayer of adsorbed species is formed on the surface of the pores.