EFFECT OF VISCOSITY ON RETENTION TIME AND HYDRODYNAMIC LIFT FORCES INSEDIMENTATION STERIC FIELD-FLOW FRACTIONATION/

Particles entrained in fluid dow between parallel bounding walls tend to be driven by hydrodynamic forces, acting perpendicular to the direc tion of how, towards certain equilibrium positions between the walls. Sedimentation held-how fractionation is a technique that is well suite d to the measurement of these forces, particularly in the regions dose to the walls. Forces much stronger than those due to fluid inertial e ffects are commonly observed in the near-wall regions. A study is pres ented here of the influence of carrier fluid viscosity on these hydrod ynamic lift forces. The carrier viscosity is varied via two different methods: (1) various ternary mixtures of water, glycerol, and ethanol were used that varied in viscosity while being of constant density and (2) the temperature of the FFF system was raised, changing the carrie r viscosity while not significantly altering its density. The near-wal l lift forces are shown to be dependent on fluid viscosity. An empiric al equation describing the apparent dependence is presented. Copyright (C) 1996 Elsevier Science Ltd