Sg. Bike et al., ELECTROKINETIC LIFT OF A SPHERE MOVING IN SLOW SHEAR-FLOW PARALLEL TOA WALL .1. EXPERIMENT, Journal of colloid and interface science, 175(2), 1995, pp. 411-421
In this paper we present experimental observations of the migration aw
ay from a wall of 9.87- and 5.2-mu m-diameter polystyrene latex sphere
s in solutions of varying viscosity and conductivity. During slow line
ar shear flow, this lateral migration is diminished by an increase in
the fluid conductivity caused either by adding salt to increase the nu
mber of charge carriers or by adding water to decrease the viscosity.
At a shear rate of 6 s(-1), for example, the largest conductivity for
which lift of 5.2-mu m spheres is observed is 0.12 mu S cm(-1). In add
ition, the increase in the particle-wall separation distance upon the
initiation of flow generally increases with particle zeta potential fo
r a given fluid conductivity. These observations support the hypothesi
s that the migration is electrokinetically induced, but predictions of
lift based on the current lubrication theory are more than one order
of magnitude weaker than gravity. This disagreement has led us to refi
ne the electrokinetic lift theory in the sequel to this paper. (C) 199
5 Academic Press, Inc.