Colloid characterization by sedimentation field-flow fractionation: V. Split outlet system for complex colloids of mixed density

Abstract

In this paper we report a new sedimentation field-flow fractionation (sedimentation FFF) methodology which can be used to characterize complex colloidal populations whose particles vary in both diameter and density (or chemical composition). By this methodology the outlet stream of the thin FFF channel is split along a specified flow plane to yield two distinguishable flow laminae whose contents enter two different outlet substreams. With a properly adjusted carrier density, the population of colloidal particles, driven by centrifugation, will divide into two subpopulations or classes, which move toward opposite channel walls and thus occupy different laminae. These subpopulations then undergo FFF migration and separation along their respective walls followed by elution into the two different substreams. This process yields the simultaneous fractionation and characterization of both subpopulations with respect to density and particle diameter values. The theory of this new technique has been developed and applicability has been demonstrated by separating and characterizing a mixture of polystyrene and polymethyl methacrylate latex beads.