Electrokinetic Lift of a Sphere Moving in Slow Shear Flow Parallel to a Wall: I. Experiment

• Published in: Journal of colloid and interface science Vol. 175; no. 2; pp. 411 - 421
• Main Authors: Bike, S.G., Lazarro, L., Prieve, D.C.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 1995; Elsevier
• Subjects: Chemistry; Colloidal state and disperse state; electrokinetic lift; Exact sciences and technology; General and physical chemistry; linear shear flow; particle migration; Physical and chemical studies. Granulometry. Electrokinetic phenomena; sphere-wall interactions; zeta potential; particle migration; sphere-wall interactions; zeta potential; electrokinetic lift; linear shear flow; Viscosity; Electrical conductivity; Microsphere; Electrical properties; Shear flow; Particle suspension; Experimental study; Latex; Particle mobility; Micron size particle; Electrokinetic potential; Styrene polymer; Spherical particle; Aqueous solution; Colloid particle; Rheological properties
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1006/jcis.1995.1471

In this paper we present experimental observations of the migration away from a wall of 9.87- and 5.2-μm-diameter polystyrene latex spheres in solutions of varying viscosity and conductivity. During slow linear shear flow, this lateral migration is diminished by an increase in the fluid conductivity caused either by adding salt to increase the number 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-μm spheres is observed is 0.12 μS cm -1. In addition, the increase in the particle-wall separation distance upon the initiation of flow generally increases with particle zeta potential for a given fluid conductivity. These observations support the hypothesis 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 refine the electrokinetic lift theory in the sequel to this paper.