Influence of accumulation wall and carrier solution composition on lift force in sedimentation/steric field-flow fractionation

Abstract

Abstract Sedimentation/steric field-flow fractionation is an established analytical technique for characterizing particulate materials by size in the approximate diameter range 1–100 μm. Particles are eluted through a thin, parallel-walled channel by a flow of a carrier liquid while a centrifugal field is applied across the thin dimension perpendicular to the flow. During elution, particles are driven towards equilibrium positions between the channel walls where the force due to the applied field is balanced by hydrodynamic lift forces. These lift forces are not yet fully characterized, and calibration using latex standards is at present a necessary prerequisite for size characterization of unknown materials. A greater understanding of the forces involved will ultimately eliminate this need for calibration. The elution of latex standards under various field strength and carrier flow rate regimes yields information on lift force as a function of particle size, flow velocity, position within the channel, and any other controllable system property. The work presented here examines the influence of channel wall and carrier solution composition (ionic strength and pH) on overall lift. It is shown that the observed lift may be described as the sum of a force due to the effects of fluid inertia, an empirical near-wall lift force inversely dependent on particle distance from the wall, and a force due to electrostatic repulsion.