COLLOIDAL INTERACTIONS IN LOW-VOLUME FRACTION PRESSURIZED ULTRAFILTRATION SYSTEMS

Attempting to use ultrafiltration as a method of preparing colloidal s uspensions of known composition for use in verifying electrokinetic th eories requires care in the determination of the bulk suspending elect rolyte concentration even at low particle volume fraction. A model of such a system is proposed to calculate the actual bulk concentrations. The work is based on the supposition that the application of the pres sure difference across the colloidal suspension in the ultrafiltration process creates a volume fraction profile within the system. When rem oved from the applied pressure, the system returns to a uniform state, but with an equivalent bulk electrolyte concentration that depends on the total particle concentration and the composition of the filtrate. This model predicts that the bulk concentration varies with volume fr action, which is qualitatively similar to experimental observation. Ho wever, the magnitude of the changes calculated were not large enough t o fully explain the experimental results; this suggests some other fac tor may also be contributing to the observed phenomena. (C) 1995 Acade mic Press, Inc.